Project library: per-project OPFS working copies with the side-panel management UI

[maboa]

The side panel returns as a project library over OPFS — the management UX of the former Recents (last-edited list, Starred section, kebab rename/duplicate/delete, current-project highlight) rebuilt against the .hyperaudio project model instead of localStorage. Successor to #434/#435/#440's UX after #451's deletion; pulls the per-project working-copy architecture forward from the Phase B umbrella (#452).

Model

• Every project (transcription, import, opened .hyperaudio) lives in work/<projectId>/ — the single-file snapshot (Save integrity: delegated edit tracking, generation guards, transactional open (#403 Phase A) #448) plus media, with a small library index (name, starred, timestamps, media meta) maintained alongside.
• The side panel lists the library: last-edited order with created-date fallback, Starred pinned above, current project highlighted, kebab actions (rename = the project title Save uses; duplicate = new id sharing nothing or copying media; delete with confirm — removes the directory).
• Switching projects asks nothing and loses nothing: the outgoing project's pending autosave flushes to its own directory. The discard-on-switch dialogs existed only because there was one work slot; they go.
• Save keeps its meaning: the .hyperaudio download is the durable, portable copy. The dirty dot and quit guard become per-project ("changes not yet saved to a file" tracked per project via its own lastDownloadAt).
• The Second-tab guard: one Web Lock, read-only banner (#403 Phase A) #450 Web Lock becomes per-project (hyperaudio:project:<id>): two tabs can edit different projects; the same project in a second tab gets the guarded banner. The origin-global lock remains for index writes.
• Identity is OPFS-native (generated ids) — none of the file↔workdir matching hazards; re-opening the same .hyperaudio twice simply creates a second library entry.

Notes

• The deleted panel UI (rows, kebab menu, star sections, inline rename) is reference material in history at v0.9.1 / pre-Delete the legacy localStorage/IndexedDB storage layer and the Recents UI (#403 Phase A) #451 — resurrect the patterns, rewire the storage calls.
• Boot: restore the most recently edited project (or none → demo); the boot hint becomes the index.
• Release hold: ships together with the Save and open projects as a single portable .hyperaudio file #403/Save/open projects as a single .hyperaudio file (#403) #404 foundation as one release, so no released version carries the management-UI gap.