feat: add dependency-free formatting/lint policy suite and root lint script (E00-S05-T01)

The formatting-policy suite (tests/formatting-policy.test.mjs) locks in the
workspace formatting and lint policy: LF line endings, no BOM, no trailing
whitespace, no tab indentation, exactly one final newline, and valid JSON
with 2-space indentation and no duplicate keys. Every rule has a mutation
probe. The root `lint` script runs the suite; the CI formatting-lint stage
executes it.

package.json

@@ -9,6 +9,7 @@
   },
   "scripts": {
     "build": "pnpm -r run build",
+    "lint": "node --test tests/formatting-policy.test.mjs",
     "test": "node --test \"tests/**/*.test.mjs\"",
     "typecheck": "pnpm -r run typecheck"
   },