Refine workspace layer edit boundary

[kostyafarber]

Summary

• Replace the old workspace edit-layer helper path with explicit glyph/layer creation and existing-layer edit methods.
• Move semantic change construction behind FontChange constructors so workspace code no longer hand-builds change payloads.
• Update bridge and renderer glyph creation to use explicit createGlyph/createGlyphLayer calls, plus regenerated bridge ID types.
• Update bridge integration tests to assert explicit creation semantics and valid TTF export setup.

Checks

• pnpm typecheck
• pnpm test
• pre-commit hook: cargo check/tests, cargo fmt, cargo clippy, oxfmt, oxlint, typecheck, deadcode, vitest