init: Cargo workspace with tala-format, tala-srs, tala-cli
Sets up a three-crate workspace for the Typst-based SRS app.
- tala-format: walks typst-syntax 0.14 LinkedNode tree to extract
CardEntry (FrontBack, Cloze, ImgCloze) with byte spans; 7 unit tests
covering IDs, dir flag, blank indexing, and span correctness
- tala-srs: sidecar JSON schema (Sidecar, CardSchedule, Schedule,
RectEntry) with load/save and orphan/missing cross-check helpers
- tala-cli: `tala check` (parse + sidecar diff) and `tala review`
(stub) driven by the two libraries
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>