feat(deps): pre-commit type-check on staged TS files

Pre-commit now runs `tsc` against the staged ts/tsx files (and their
dep graph) in ~3s, catching type errors before they hit CI. Used to
skip type-check entirely on pre-commit because full-project tsc is
~22s — too slow for the commit hook.

Drops a 30-LOC shim in `scripts/tsc-staged.mjs` instead of the
`tsc-files` package: that lib's binary-resolution path
(`typescript/../.bin/tsc`) doesn't exist under pnpm's virtual-store
layout, so spawnSync returns `status: null` and the check silently
no-ops. Filed upstream-style: the package hasn't shipped in 3 years.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.lintstagedrc.json

@@ -1,4 +1,4 @@
 {
-  "*.{ts,tsx}": ["eslint --fix", "prettier --write"],
+  "*.{ts,tsx}": ["eslint --fix", "prettier --write", "node scripts/tsc-staged.mjs"],
   "*.{json,md,css}": ["prettier --write"]
 }