Introduce renderer FontStore glyph snapshots

[kostyafarber]

Summary

• Add renderer-owned FontStore for workspace summary records, loaded glyph snapshots, snapshot status, stable model identity, and pending local commits.
• Rename WorkspaceEditQueue to WorkspaceSync and make it own async apply/undo/redo/save/snapshot ordering while WorkspaceSession stays transport-only.
• Replace layer-addressed snapshot reads with bounded glyph/source workspace.glyphSnapshots requests through the shared protocol, bridge types, NAPI bridge, WorkspaceHost, and WorkspaceSession.
• Keep variation data on the glyph snapshot, not layer state; layer state remains structure + values only.
• Move route, grid preview, and text-entry snapshot hydration behind the editor-owned GlyphSnapshotLoader boundary so UI/model getters remain synchronous.
• Tighten FontStore, GlyphSnapshotLoader, and Font model API boundaries with explicit sync/load/glyph-snapshot ports and id-based glyph/layer reads; guard stale/failed snapshot responses by workspace generation.

Verification

• pnpm --filter @shift/desktop run typecheck
• pnpm --filter @shift/desktop run lint:check
• pnpm run format:check
• pnpm --filter @shift/desktop exec vitest run src/renderer/src/lib/model/GlyphSnapshotLoader.test.ts src/renderer/src/lib/model/FontStore.test.ts
• GitHub Actions CI manual run on 337cda9: required CI Passed gate succeeded, including Unit Tests and Integration Tests. https://github.com/shift-editor/shift/actions/runs/27920122677
• Blocked locally: broader Vitest suites that import shift-bridge cannot collect because shift-bridge-linux-x64-gnu / cargo are missing in this environment.