feat(history): concept heading and summary

The Prompt history page takes the approved mock's heading and summary
surface (docs/concepts/workspace/app.js renderHistory a591-598, #249 F1):

- Heading description is "Prompt history · one positive, one shared
  gallery"; the actions stay "← Prompt library", "Edit metadata" and
  button.send "Send to ComfyUI" (aria-label "Send prompt pair to ComfyUI:
  <title>"), on one row at 1600. Send is disabled only while the selected
  pair's roles are loading (D24).
- The summary is article.surface > span.chip category, the positive and
  selected negative prompt blocks, then .card-meta "N tracked runs · N
  images · N negative variants". Tracked runs come from the recorded
  history window's recorded_run_count (hidden until a read completes,
  kept while a refresh is in flight); images and variants from the
  saved positive's image_count and variant_count.
- The summary's copy/send actions are named after the prompt, as in the
  concept ("Copy positive prompt: <title>"); mountPromptBlocks gains
  setTitle so an in-place metadata edit renames them without a remount.
- mountRecordedHistory gains an optional onRecordedCount callback.

Selector mapping:
- .library-surface (history summary)  -> .library-history article.surface
- .library-surface .library-chip      -> article.surface > span.chip
- "Copy|Send <role> prompt[ to ComfyUI]" in "Saved prompt texts"
                                      -> "...: <title>"
- heading p.muted "One positive prompt. Reusable negative variants. One
  shared gallery." -> "Prompt history · one positive, one shared gallery"
- Unchanged: region "Saved prompt texts", .library-variants,
  .library-shared-gallery, .recorded-history (still .library-surface).

Tests: workspace-history "history heading actions stay on one row at 1600
and are enabled after load" and "summary meta uses recorded runs" (both
failed before), a prompt-blocks setTitle unit, and the mapped selectors in
workspace-visual, workspace-library-editor and the canonical comparison.

web/js/workspace/workspace.css

@@ -214,6 +214,9 @@ pre.prompt-text { font: inherit; font-size: 12px; line-height: 1.75; white-space
 .prompt-card .prompt-text { display: -webkit-box; -webkit-box-orient: vertical; -webkit-line-clamp: 2; line-clamp: 2; overflow: hidden; /* D23 */ }
 /* #249 D23: the prompt blocks' mount point is transparent, so the section sits in `.card-content` as the concept's does. */
 .card-content > .prompt-inspector { display: contents; /* D23 */ }
+/* #249 D24: the history summary's prompt blocks sit in `article.surface` as the concept's do (app.js a598); the mount
+   point keeps its "Saved prompt texts" region name. */
+.library-history article.surface > .prompt-inspector { display: contents; /* D24 */ }
 /* #249 D23: a real title can be long or one unbroken word; it wraps inside the title row (the toolkit's buttons never
    wrap), while the category chip keeps whole words beside it and wraps only a name wider than its share of the row. */
 .card-title button { min-width: 0; white-space: normal; overflow-wrap: anywhere; /* D23 */ }