fix: Enable strict lint enforcement with correct path matching

BREAKING CHANGE: Strict lint enforcement is now ACTIVE

Pre-commit hooks now block commits if:
- Affected package has ANY lint errors or warnings
- Affected package has ANY type errors

Impact: If you touch a file in a package with existing violations,
you MUST fix ALL violations in that package before committing.

This forces incremental cleanup:
- Work in @mosaic/shared → Fix all @mosaic/shared violations
- Work in @mosaic/api → Fix all @mosaic/api violations
- Work in clean packages → No extra work required

Fixed regex to handle absolute paths from lint-staged.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.lintstagedrc.mjs

@@ -13,9 +13,11 @@ export default {
     // 1. Format first (auto-fixes what it can)
     commands.push(`prettier --write ${filenames.join(' ')}`);
 
-    // 2. Extract affected packages
+    // 2. Extract affected packages from absolute paths
+    // lint-staged passes absolute paths, so we need to extract the relative part
     const packages = [...new Set(filenames.map(f => {
-      const match = f.match(/^(apps|packages)\/([^/]+)\//);
+      // Match either absolute or relative paths: .../packages/shared/... or packages/shared/...
+      const match = f.match(/(?:^|\/)(apps|packages)\/([^/]+)\//);
       if (!match) return null;
       // Return package name format for turbo (e.g., "@mosaic/api")
       return `@mosaic/${match[2]}`;
@@ -26,7 +28,7 @@ export default {
     }
 
     // 3. Lint entire affected packages via turbo
-    // --max-warnings=0 means ANY warning blocks the commit
+    // --max-warnings=0 means ANY warning/error blocks the commit
     packages.forEach(pkg => {
       commands.push(`pnpm turbo run lint --filter=${pkg} -- --max-warnings=0`);
     });