feat(collections): COLLECTIONS sidebar, collection page and saved views (#331, PR 2) (#410)

* feat(saved-views): keep a collection in a saved view

Images saved views gain a collection key (#331 D140): empty or a collection
id of 1 to 9 digits. Writes refuse favorites together with a collection;
older rows read an empty collection, and a stored row with both opens the
collection, as the listing does for a URL with both.

Part of #331

* feat(collections): store collections in the library database

* feat(collections): add, remove and rename collections and keep members through duplicate cleanup

* feat(collections): add collection routes and the Images collection filter

* feat(images): store images' own categories in the library database (#332)

One new table, image_categories, and its category index, created empty
by a forward-only migration that reads and writes only its own objects.
Startup checks the structure; restore also checks the values. The store
sets, clears and reads own categories by file key (the deepest output
source holding the file and the path below it), and copies a removed
duplicate's category to a kept copy that has none.

* feat(images): duplicate cleanup keeps images' own categories (#332)

The kept copy's own category wins; a kept copy without one receives the
removed copy's, keyed by the deepest output source holding each file.
The removed copy's row is never deleted, so a give-back or a failed
delete loses nothing. The job log reports how many were kept.

* feat(images): set, remove and list images' own categories (#332)

PUT /prompt_manager/images/category sets the own category of up to 500
listed files, DELETE removes it (listed or not), and
GET /prompt_manager/images/categories lists the values whose file is
listed. Targets are the Images listing identity of an output source,
checked by media_target (shared with Collections). The routes never
touch prompts, recipes or links; POST /prompt_manager/bulk/category is
unchanged.

* fix(images): key symlinked output folders and keep key work off the event loop (#332)

Review fixes: a source matches by its configured spelling too, so a
detected output folder that is a symlink keys its files (routes and
duplicate cleanup). File keys are computed in the executor. A path no
source holds is a plain 403, a lone surrogate a 400. The install repairs
a table that lacks its category index instead of refusing to open.

* fix(collections): address review findings

* feat(images): set or remove a category on all N matching images (#332)

The category routes also accept the Images listing filter of "Select
all N matching" (#392) instead of explicit items, resolved now and
capped at 500 images like an explicit selection.

* feat(collections): browse a collection from the sidebar

The sidebar gains the concept's COLLECTIONS group (D136): one row per
collection with its folder icon, name and listed-member count, without the
PROPOSED badge; the label shows once a collection exists. A row opens
#/collection/<id>, the Images page filtered to that collection (D137): the
collection's name as h1, Collection as breadcrumb and title, Edit to rename
or delete it through the saved views' Edit dialog with collection nouns, and
a note counting members the sources do not list now. An unknown or deleted
collection shows a page that says so with a link to Images. A saved view on
a deleted collection lists nothing and says so (MC6, D140). The list is read
again after a restore and the counts 300 ms after a change.

Part of #331

* test(collections): compare the COLLECTIONS group with the concept

The concept hides COLLECTIONS at 950 px and below, which would leave a phone
no way to open a collection; production shows the rows there in the wrapped
layout of every other sidebar nav (D136). The shell comparison now compares
the group instead of filtering it out: the concept fixture seeds Landscapes
(12) and Experiments (8), the rows compare by name order, and at phone width
the nav compares against the concept's own sidebar-nav layout. The
collection rows are checked at 1600x1100 and 390x844 in both themes.

Part of #331

* test(vendor): count the #332 host case in the execution matrix

image-attribution.spec.mjs gains the image category route case, so the
execution config lists 92 tests (3 attribution cases per project).

* test(browser): install the slideshow clock before wrapping setTimeout

The slideshow fixture wrapped window.setTimeout before page.clock.install(),
so the viewer's timer ran on real time and clock.runFor() did not drive it;
a late WebKit timer failed 'slideshow exposes exact state labels' on CI.

* fix(collections): address review findings

- A list read superseded by a newer one (the 300 ms count read, a restore)
  no longer shows "could not be loaded": the collection and saved-view
  pages wait for the list to settle.
- A listing that finds the open collection gone shows the deleted page once
  the list no longer holds it; when the list read fails or still holds it,
  the page keeps the listing's error and Retry instead of staying blank, and
  each failed read is reported again.
- The missing-members note follows every list read and goes away at zero.
- A rename that settles after its Edit dialog closed leaves any dialog
  opened since alone.
- The deleted-collection, list-failed and saved-view failure pages focus
  their title after a route change, as every page does.

Part of #331

* test(coverage): keep main's floors for files this PR does not touch

coverage:update raised nine floors of untouched files from one run;
metadata-autocomplete.js branches then measured 84.84 against 85.

* test(legacy): record the image category routes in the legacy contract snapshot (#332)

#332 adds PUT/DELETE /prompt_manager/images/category and
GET /prompt_manager/images/categories; the legacy pages' routes are
unchanged.

* test(duplicates): a removed copy with a collection and a category moves both (#331, #332)

database/saved_views.py

@@ -35,6 +35,9 @@ _LIBRARY_SORTS = ("newest", "oldest", "name", "rating")
 _MEDIA = ("all", "image", "video")
 _CONTROL = re.compile(r"[\x00-\x1f\x7f]")
 _SOURCE = re.compile(r"all|0|[1-9][0-9]{0,8}")
+# A collection id as the listing's ``collection`` query takes it (#331): none
+# ("") or 1 to 9 digits without a leading zero.
+_COLLECTION = re.compile(r"|[1-9][0-9]{0,8}")
 FALLBACK_NAME = "Saved view"
 
 
@@ -55,6 +58,9 @@ _STATE_FIELDS = {
         "tags": ("tags", None, ()),
         # The Favorites page's filter (#249 D51): a view saved there reopens it.
         "favorites": ("bool", None, False),
+        # A view saved on a collection page (#331 D140) reopens that
+        # collection; never together with favorites.
+        "collection": ("collection", None, ""),
     },
     "library": {
         "q": ("text", 500, ""),
@@ -125,6 +131,8 @@ def _validate_value(key: str, kind: str, limit, value: object) -> None:
         raise SavedViewInvalid(f"State '{key}' is not a supported value")
     if kind == "source" and not _SOURCE.fullmatch(value):
         raise SavedViewInvalid(f"State '{key}' must be 'all' or a source index")
+    if kind == "collection" and not _COLLECTION.fullmatch(value):
+        raise SavedViewInvalid(f"State '{key}' must be empty or a collection id")
     if kind == "text" and (len(value) > limit or _CONTROL.search(value)):
         raise SavedViewInvalid(f"State '{key}' is too long or has control characters")
 
@@ -142,6 +150,8 @@ def encode_state(page: object, state: object) -> str:
         )
     for key, (kind, limit, _default) in fields.items():
         _validate_value(key, kind, limit, state[key])
+    if state.get("favorites") is True and state.get("collection"):
+        raise SavedViewInvalid("A view cannot filter by favorites and a collection")
     encoded = json.dumps(
         {key: state[key] for key in fields}, ensure_ascii=False, separators=(",", ":")
     )
@@ -181,6 +191,10 @@ def normalize_state(page: str, raw: object) -> dict:
         except SavedViewInvalid:
             value = default
         state[key] = list(value) if kind == "tags" else value
+    # Never written by this build; a stored row with both opens the collection,
+    # as the listing does for a URL with both (#331 D140).
+    if state.get("favorites") is True and state.get("collection"):
+        state["favorites"] = False
     return state