Improve AI filtering error handling and visibility

- Add listAvailableModels() and validateModel() to openai.ts
- Improve testOpenAIConnection() to test configured model
- Add checkAIStatus endpoint to filtering router
- Add pre-execution AI config check in executeRules
- Improve error messages in AI filtering service (rate limit, quota, etc.)
- Add AI status warning banner on round detail page for filtering rounds

Now admins get clear errors when AI is misconfigured instead of silent flags.

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

src/server/services/ai-filtering.ts

@@ -383,13 +383,40 @@ Return your evaluation as JSON.`
       }
     }
   } catch (error) {
-    // OpenAI error — flag all for manual review
+    // OpenAI error — flag all for manual review with specific error info
     console.error('[AI Filtering] OpenAI API error:', error)
+
+    // Extract meaningful error message
+    let errorType = 'unknown_error'
+    let errorDetail = 'Unknown error occurred'
+
+    if (error instanceof Error) {
+      const message = error.message.toLowerCase()
+      if (message.includes('rate_limit') || message.includes('rate limit')) {
+        errorType = 'rate_limit'
+        errorDetail = 'OpenAI rate limit exceeded. Try again in a few minutes.'
+      } else if (message.includes('model') && (message.includes('not found') || message.includes('does not exist'))) {
+        errorType = 'model_not_found'
+        errorDetail = 'The configured AI model is not available. Check Settings → AI.'
+      } else if (message.includes('insufficient_quota') || message.includes('quota')) {
+        errorType = 'quota_exceeded'
+        errorDetail = 'OpenAI API quota exceeded. Check your billing settings.'
+      } else if (message.includes('invalid_api_key') || message.includes('unauthorized')) {
+        errorType = 'invalid_api_key'
+        errorDetail = 'Invalid OpenAI API key. Check Settings → AI.'
+      } else if (message.includes('context_length') || message.includes('token')) {
+        errorType = 'context_length'
+        errorDetail = 'Request too large. Try with fewer projects or shorter descriptions.'
+      } else {
+        errorDetail = error.message
+      }
+    }
+
     for (const p of projects) {
       results.set(p.id, {
         meetsCriteria: false,
         confidence: 0,
-        reasoning: `AI screening error — flagged for manual review`,
+        reasoning: `AI screening error (${errorType}): ${errorDetail}`,
         qualityScore: 5,
         spamRisk: false,
       })