[codex] Add workspace font change sets

[kostyafarber]

What changed

• Added shift-font semantic font change records for committed edit deltas.
• Added shift-store.apply_change_set(...) and outline row storage for glyph unicodes, layer metrics, contours, and points.
• Routed FontWorkspace commits through store application before swapping the live font.
• Updated bridge mutation paths to describe their durable semantic changes, using incremental changes for common edits and LayerGeometryReplaced as the fallback for broader geometry rebuilds.

Why

This moves the Rust workspace toward the durable local-first runtime design: committed editor operations become semantic change sets, and shift-store applies them transactionally instead of treating persistence as a whole-font or whole-layer snapshot path.

Validation

Pre-commit ran and passed:

• cargo check including tests
• cargo fmt
• cargo clippy
• cargo test

Additional focused checks run before committing:

• cargo test -p shift-store
• cargo test -p shift-bridge
• cargo test -p shift-font
• cargo test -p shift-workspace
• cargo check -p shift-font -p shift-store -p shift-workspace -p shift-bridge
• git diff --check