fix(moderation): patch 6 aiAnalyzer audit vulnerabilities

#1+#5 - Individual fallback circuit breaker
  - Add individualConsecutiveErrors + individualCooldownUntil (30s)
  - On success: reset counter; on failure: increment + trip at
    AI_ANALYSIS_INDIVIDUAL_CB_THRESHOLD (default 10) consecutive errors
  - enqueueIndividualFallbacks checks CB before admitting any work

#1 - Individual fallback concurrency cap
  - enqueueIndividualFallbacks enforces AI_ANALYSIS_INDIVIDUAL_MAX_CONCURRENT
    (default 20); overflow stays as error/analysis_incomplete in DB and is
    recovered by the recovery worker on the next interval

#3 - Unhandled rejection in async setTimeout
  - scheduleConversationAnalysis no longer uses async arrow in setTimeout;
    all async work is chained with .then()/.catch() explicitly

#4 - Recovery worker ignores individualInFlight
  - Add individualInFlightByConversation Map<conversationKey, count>
  - processIndividualFallback increments/decrements it in try/finally
  - startPendingAIAnalysisWorker skips conversations present in the map
  - Recovery worker also processes error/analysis_incomplete messages via
    two new messageStore queries: getConversationKeysWithIncompleteAnalysis
    and getIncompleteMessagesByConversation

#6 - pickBatchWithinBudget never called
  - scheduleConversationAnalysis now calls pickBatchWithinBudget with
    AI_ANALYSIS_MAX_TARGET_TOKENS (default 4000) + 50-token per-msg overhead
    after fetching messages, before passing to processBatch

#7 - AI_PROCESSING_OVERLAP_MS 30s shorter than max LLM retry window
  - Replace hardcoded 30 000 ms constant with configurable
    AI_ANALYSIS_PROCESSING_TIMEOUT_MS (default 120 000 ms)
  - LLM client: 30s timeout × 3 retries + backoff ≈ 90-100s; 120s is safe

New config keys:
  AI_ANALYSIS_PROCESSING_TIMEOUT_MS   (default: 120000)
  AI_ANALYSIS_INDIVIDUAL_MAX_CONCURRENT (default: 20)
  AI_ANALYSIS_INDIVIDUAL_CB_THRESHOLD  (default: 10)
  AI_ANALYSIS_MAX_TARGET_TOKENS        (default: 4000)

New AnalysisQueueStatus fields:
  activeIndividualRequests, individualInFlightCount,
  individualCircuitBreakerActive

src/moderation/types.ts

@@ -141,5 +141,7 @@ export interface AnalysisQueueStatus {
   activeIndividualRequests: number;
   /** Number of message IDs sitting in the dedup set (in-flight or about to start). */
   individualInFlightCount: number;
+  /** True when the individual-fallback circuit breaker is tripped. */
+  individualCircuitBreakerActive: boolean;
   lastError: string | null;
 }