Move the edit tool's hot-path diffing operations from JS to native Rust:
- `normalizeForFuzzyMatch`: single-pass Unicode normalization (smart quotes,
dashes, special spaces, trailing whitespace)
- `fuzzyFindText`: exact-then-fuzzy substring search with UTF-16 index
conversion for JS compatibility
- `generateDiff`: unified diff generation using the `similar` crate
(Myers' algorithm with optimizations)
The Rust module at `native/crates/engine/src/diff.rs` exposes three napi
functions. The TypeScript wrapper at `packages/native/src/diff/` follows
the existing module pattern. `edit-diff.ts` now delegates to native
implementations while keeping line-ending handling and file I/O in JS.
18 tests covering normalization, fuzzy matching (including UTF-16 index
correctness with emoji/surrogate pairs), and diff generation.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
