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)

tests/browser/workspace_visual_fixture.py

@@ -112,6 +112,8 @@ def seed_workspace_visual(api: PromptManagerAPI, root: Path) -> None:
     """Replace only the owned browser harness records and media roots."""
     with api.db.model.get_connection() as conn:
         for table in (
+            "image_collection_items",
+            "image_collections",
             "saved_views",
             "image_favorites",
             "media_review_decisions",