Consolidate font model into shift-font

[kostyafarber]

Summary

Consolidates the Rust font model around shift-font and removes the old shift-edit / shift-ir split.

• moves the reusable edit/model code into shift-font
• moves bridge DTO-oriented interpolation/state helpers into shift-wire
• updates downstream Rust crates to depend on shift-font
• removes bridge-owned active edit sessions in favor of explicit GlyphLayerRef mutation targets
• updates renderer bridge calls, generated TypeScript bridge types, tests, docs, and scripts

Why

This gives the next workspace/store work a cleaner base: shift-font is now the first-class object model, bridge mutation no longer depends on hidden native session state, and renderer selection stays explicit.

Validation

• cargo check --workspace
• cargo test --workspace
• pnpm typecheck
• pnpm --filter shift-bridge run test
• pnpm --filter @shift/desktop test -- Glyph.test.ts variation.test.ts SourceEditDraft.test.ts ApplyPositionPatchCommand.test.ts
• commit hooks: cargo check, cargo fmt, cargo clippy, cargo test, oxfmt, oxlint, tsgo typecheck, deadcode, vitest

Notes

python3 scripts/context-drift-check.py was not run because the local Python environment is missing markdown_it.