M8: PDF export, named snapshots, and per-user undo

[pedrobritx]

Summary

Implements NotUX M8 — the three features the Home screen already advertises ("Sign in for named snapshots & PDF export"):

1. Per-user, board-wide undo
2. Named snapshots (save / list / restore)
3. PDF export (current page or all pages)

No SQL migration required — the existing boards/snapshots policies already support owner-claim + named inserts once a boards row exists.

Per-user undo

• New LOCAL_ORIGIN symbol in @notux/sync, threaded through every user-initiated transaction: shapeStore (addShape/updateShape/deleteShape/deleteShapes/transact) and pageList (add/remove/rename/move). Seed-page creation and page-map auto-creation stay untracked so a fresh user's first Ctrl+Z can't delete the only page.
• useUndoManager rewritten from a per-page manager to a single board-wide one tracking getMap("pages") + getArray("pageList") with trackedOrigins = {LOCAL_ORIGIN}. History now survives page switches, and remote peers' edits / IndexedDB hydration (different origins) are never captured — undo is genuinely per-user in multiplayer. captureTimeout: 300 coalesces drag bursts.

Named snapshots

• ensureBoardOwnership claims an unowned boards row on load (signed in) so the owner-gated named-snapshot insert passes RLS.
• snapshots.ts: encodeSnapshot (Y.encodeStateAsUpdate) and restoreSnapshot, which rebuilds pages + pageList in one LOCAL_ORIGIN transaction — so a restore broadcasts to peers and is undoable in a single step. pageStore's observer already handles the active page disappearing.
• snapshotsApi.ts stores ydoc as a PostgREST \x hex bytea (no server-side decode RPC needed).
• SnapshotsPanel UI (save label / list with relative time / restore-with-confirm), wired into the app-menu File section. Owner-gated; clear messaging in local-only / signed-out / non-owner states.

PDF export

• Adds jspdf (dynamically imported, code-split into its own chunk).
• renderPageToCanvas mounts a detached react-konva Stage reusing ShapesLayer (pixel-parity, no renderer reimplementation), cropped to the page's content bounding box + padding. Asset bitmaps are pre-warmed and readiness is polled (one Konva Image per asset shape) with a 3s timeout fallback.
• exportBoardToPdf assembles one PDF page per non-empty board page (empty pages skipped; one blank page if all empty). Menu offers a current page / all pages chooser. Works in local-only mode.

Verification

• pnpm -r typecheck ✅ and pnpm build ✅ (jspdf isolated in its own dynamic chunk).
• Manual (suggested): two tabs → confirm undo only reverts the local tab's edits and survives page switches; sign in → save/restore a snapshot (reverts in both tabs, undoable in one step); export current/all pages to PDF cropped to content with assets rendered.

🤖 Generated with Claude Code

https://claude.ai/code/session_01J9ed2Wi8rXZZz1bHFDwAVa

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Generated by Claude Code