Use reusable glyph projections for renderer views

[kostyafarber]

Summary

• replace location-resolved glyph preview payloads with compact, location-independent GlyphProjection backing from shift-font through the workspace bridge
• introduce reactive GlyphView objects that use live authored layers when available and local interpolation otherwise, including exact incompatible source shapes and recursive components
• share interpolation-basis weights across glyphs with the same compatible source set; numeric edits stay in the existing signal graph while structural changes refresh resident projections atomically
• make the virtualized grid coalesce projection reads by glyph identity, retain loaded backing across scrolling, and scrub locally without IPC or location-keyed caches
• use the same derived advance in text positioning, removing the interpolated x-advance jump
• document the loading, ownership, invalidation, and naming invariants for future renderer work

Related to #50.

Verification

• pnpm test:unit — 494 desktop tests passed
• pnpm typecheck
• pnpm lint:check
• pnpm format:check
• pnpm deadcode:strict
• cargo test -p shift-font -p shift-wire -p shift-bridge — 199 tests passed
• cargo clippy --workspace --all-targets -- -D warnings
• commit hooks passed in full

python3 scripts/context-drift-check.py still reports the 15 existing repository documentation errors; the new renderer-model route is valid and adds no new drift error.