Move glyph interpolation into shift-font

[kostyafarber]

Summary

• move canonical glyph interpolation values, source compatibility, variation-model construction, and evaluation into shift-font
• add FontProjection and ResolvedGlyph as a location-bound read-only projection with exact-source, interpolation, sparse fallback, and recursive component semantics
• reduce shift-wire to adapting native interpolation into renderer DTOs, and remove the leaked GlyphMaster NAPI/TypeScript contract
• document the new ownership boundary in the canonical font and bridge docs

Why

Issue #150 needs a lightweight batch preview built on a canonical Rust projection. Previously, interpolation semantics and flattened glyph values were partly owned by shift-wire, which made a preview resolver either duplicate that logic or turn a transport crate into a domain service.

This PR gives shift-font one native projection API that the preview bridge can consume in a follow-up. It intentionally does not add preview DTOs, workspace transport, TanStack Query integration, or grid UI.

Resolution semantics

• an exact authored master layer wins
• otherwise compatible source layers interpolate at the internal authoring location
• unavailable interpolation falls back to the default/preferred authored layer
• components resolve recursively at the same location and cyclic branches are skipped locally
• existing blank glyphs remain present with empty contours and their advance; missing IDs are omitted
• external axis mappings must be applied before constructing a projection

Validation

• pre-commit suite: Cargo check/fmt/Clippy/tests, Oxfmt, Oxlint, tsgo, dead-code checks, and Vitest
• pnpm test: all Turbo test tasks passed, including 503 desktop tests
• pnpm typecheck
• cargo clippy --workspace --all-targets -- -D warnings
• Rustdoc broken-link validation across the workspace
• documentation drift check reports only the repository's 15 pre-existing errors; the changed docs introduce none

Foundation for #150; does not close it.

[kostyafarber]

should we make location impl equality? instead or use traits