sync: stale skill detection, sentry filtering, claim removal, review improvements

Stale Detection:
- Detect skills removed/moved from GitHub (3 consecutive 404s threshold)
- Hide stale skills from browse/search, show warning banner on detail page
- Serve cached files with isStale flag when GitHub returns 404
- Add stale-check crawler command for batch verification
- CLI shows warning when installing stale skills from cache

Sentry & Error Handling:
- Filter browser extension errors and add denyUrls
- Anti-inflation measures and sentinel recalibration for curation

Claim & Removal:
- Enhanced ClaimForm with repo-level removal support
- Add repo-removal-request API endpoint with tests
- Improved owner page with bilingual content

Review Pipeline:
- Review version and reviewer tracking in submit API
- Source format filter for pending reviews
- Updated review tests

Other:
- Updated i18n strings (en/fa)
- BrowseFilters improvements
- Dockerfile updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/indexer/src/skill-indexer.ts

@@ -33,7 +33,28 @@ export async function indexSkill(
 
   // Fetch skill content
   console.log(`Fetching ${source.owner}/${source.repo}/${source.path} [${sourceFormat}]...`);
-  const content = await crawler.fetchSkillContent(source);
+  let content;
+  try {
+    content = await crawler.fetchSkillContent(source);
+  } catch (error) {
+    const errorMsg = error instanceof Error ? error.message : String(error);
+
+    // Detect 404 (skill removed from GitHub) — increment stale check
+    if (errorMsg.includes('not found') || errorMsg.includes('Not Found') || errorMsg.includes('404')) {
+      const skillName = source.path.split('/').pop() || 'skill';
+      const formatSuffix = sourceFormat !== 'skill.md' ? `~${sourceFormat.replace('.', '')}` : '';
+      const skillId = `${source.owner}/${source.repo}/${skillName}${formatSuffix}`;
+
+      await skillQueries.incrementStaleCheck(database, skillId).catch((err) => {
+        console.warn(`  -> Failed to increment stale check for ${skillId}:`, err);
+      });
+      console.log(`  -> ${skillId}: GitHub 404 (stale check incremented)`);
+      return null;
+    }
+
+    // For non-404 errors, rethrow
+    throw error;
+  }
 
   // Analyze the skill with format awareness
   const analysis = await analyzer.analyze(content, sourceFormat);