Rework the Library popover: usable default size, search auto-expand, drag-resizable height

[OmarB97]

Builds on feat/chat-context-lineage (PR #246, still open), which itself builds on feat/desktop-ergonomics (PR #245) -- same head-branch-per-PR-against-main pattern as #242/#243/#244/#246. Scoped entirely to the Library popover in the Generate area; doesn't touch anything #246 changed.

Problem

The Library popover from #243/#245 works, but the operator flagged it as unusable in real sessions:

• The row list was capped at max-h-64 (256px) -- with the 80px thumbnail tiles from Add Library thumbnail previews and a resizable panel #243, that's only 2-3 visible rows, in a popup that itself doesn't grow past its content.
• Only the panel's width was resizable; there was no way to make it taller.
• Typing a search query filters correctly, but the collapsed WORKFLOWS/EXPORTS and per-capability groups stay collapsed -- a match hiding inside a collapsed group requires clicking "Show" on every ancestor group by hand before it's visible.
• The search <input type="search"> renders as a tall box with the placeholder vertically centered in the middle of it, instead of a normal single-line field -- a Chromium input[type=search] quirk this codebase never worked around (every other input in this file is type="number"/type="text"-shaped and unaffected).

Changes

• Search auto-expands matches. isAssetLibrarySectionExpanded(collapsedSectionKeys, sectionKey, hasActiveSearch) in assetLibraryUi.ts renders a section expanded when either the user left it expanded or a search is active. collapsedSectionKeys itself is never touched by searching, so clearing the query falls straight back to whatever was collapsed before -- no extra state to keep in sync. The per-section Show/Hide toggle is disabled while a search is active (every visible group already only contains matches, so toggling it would be a dead click that silently changes post-clear state).
• The listing area now flexes instead of clipping. The row list is flex-1 min-h-0 overflow-y-auto overflow-x-hidden inside a popup with an explicit height (from state), rather than a fixed max-h-64 inside a content-sized popup. The three loading/empty/no-match placeholder states get the same flex-1 treatment so the popup doesn't collapse to a sliver when there's nothing to show.
• Height is now drag-resizable and persisted, mirroring the existing width handle exactly: a second edge handle (cursor-row-resize, bottom edge) plus clampAssetLibraryPanelHeight/getStoredAssetLibraryPanelHeight/storeAssetLibraryPanelHeight in assetLibraryUi.ts, same shape as the width triple, under its own modly-library-panel-height localStorage key. Min/max/default: 280/1000/860.
• Thumbnail tile shrunk 80px -> 40px, row padding py-2 -> py-1.5. With 80px tiles, even an 860px-tall popup (near the practical ceiling for a 1080p window before it risks running off-screen) only fits ~4 rows -- nowhere near "a dozen." Shrinking the tile is the only way to reconcile "keep thumbnail tiles" with "usable default size"; everything else about the tile (rounding, border, object-contain) is unchanged. At the new size the default popup shows 8-9 full rows before scrolling.
• Search input fix: added appearance-none to the type="search" field, matching the plain box model every other input in this file already gets natively.
• Incidental fix: the row's display-name span had no truncate/shrink-0 pairing with its capability badge, so a long filename could overflow the row width and force the scroll container into overflow-x: auto (a real single-row case reproduced a visible horizontal scrollbar during verification, sitting right below the intended vertical-only scrollbar). Added truncate to the name and shrink-0 to the badge, plus explicit overflow-x-hidden on the list container as a backstop.

Files changed

• src/areas/generate/assetLibraryUi.ts -- isAssetLibrarySectionExpanded; height clamp/get/store triple + constants.
• src/areas/generate/GeneratePage.tsx -- popup height state/effect/drag handler; search-aware expand + disabled toggle wiring; flex-based list region; smaller thumbnail/tighter row padding; appearance-none on the search input; truncate/shrink-0 on the row text row.
• src/areas/generate/assetLibraryUi.test.ts -- tests for the new height helpers and isAssetLibrarySectionExpanded (searching forces expansion; clearing falls back to the untouched collapsed-key list).

Verification

Built, packaged (npm run package, AppImage target), and installed the same way the currently-running build was installed (asar extracted into resources/app, original parked as app.asar.orig), replacing the running app on the operator's desktop.

• Typed "villain" (an asset that exists under both Workflows and Exports) into the search field with both groups collapsed beforehand -- WORKFLOWS > Rigged mesh and EXPORTS > Mesh expanded immediately, no clicks, and the search box rendered as a normal single-line field instead of the old tall box. Cleared the field -- both groups fell back to collapsed.
• With a cleared localStorage (first-run state), opened the popup and expanded Workflows > Mesh: all 9 entries in that group render fully visible with no scrolling, plus the next group's header peeking in -- up from 2-3 clipped rows before this change.
• Dragged the new bottom-edge handle down; the popup grew past its default height and revealed the next two group headers that had been below the fold.
• Killed and relaunched the app: the popup reopened at the same dragged (non-default) height, not the 860px default.
• Selected an entry post-search and confirmed "Open selected asset" still enables and the status line still updates, to make sure the open flow survived the surrounding JSX changes.
• npm run lint and npm test (23 Python + 40 Node, including the 3 new assetLibraryUi tests) both pass.

Test plan

• npm run lint
• npm test
• npm run build
• npm run package (AppImage) + real install + manual verification on the desktop app