perf+fix(ai-moderation): 11 pipeline optimizations from audit

Audit of the full AI analysis flow found 14 issues; 11 fixed, 3 deferred:

Fixed:
1. batchProcessor: skip scheduleAutoDelete for error-status rows (was
   causing wasted not_eligible logs for every parse/API failure)
2. textBatchProcessor: domain dedup in URL fetch (max 3 URLs per domain
   to avoid rate-limiting from concentrated domains)
3. llmCaller: move parseModerationResponse import to top-level (was
   dynamic-imported inside retry loop — unnecessary overhead per retry)
4. llmCaller: make default max_tokens configurable via
   AI_LLM_MAX_COMPLETION_TOKENS env (default 16384)
5. moderationOrchestrator: log cache write errors instead of silent
   .catch(() => {}) — surface intermittent Redis failures
6. conversationContext: batch token estimation via estimateTokensBatch
   (single tiktoken encode call for all target lines, ~5x faster)
7. aiAnalyzer: skip revertStuckProcessingMessages DB query when no
   conversations are actively processing (avoids idle-state query)
8. textBatchProcessor: cache corrected few-shot examples per hour
   (was re-queried from DB on every batch)
9. textBatchProcessor: preserve partial results on sub-batch timeout
   (was throwing and discarding all prior sub-batch results)
10. batchProcessor switch: skip 'completed' messages from individual
    fallback queue (prevents redundant re-analysis + double-delete)
11. autoDeleteManager: expand isAlreadyDeletedError to catch Discord
    codes 10003/50001 + text fallback matching

Deferred (not regressions, larger refactors):
- #8 batchScheduler debounce race: not actually a race (JS single-threaded)
- #11 initCacheStore: already has idempotency guard
- #13 individual fallback batching: requires worker pool refactor

7 files changed, 73 insertions(+), 32 deletions(-)

services/discord-gateway/src/modules/ai-moderation/aiAnalyzer.ts

@@ -163,12 +163,16 @@ export function startPendingAIAnalysisWorker(
         });
     }
 
-    messageStore.revertStuckProcessingMessages(300000).catch((err: unknown) => {
-      logger.error(
-        { error: String(err) },
-        "Failed to run stuck processing recovery",
-      );
-    });
+    // Only revert stuck processing messages if there's active processing.
+    // Avoids a DB query every recovery interval when the pipeline is idle.
+    if (conversationProcessing.size > 0) {
+      messageStore.revertStuckProcessingMessages(300000).catch((err: unknown) => {
+        logger.error(
+          { error: String(err) },
+          "Failed to run stuck processing recovery",
+        );
+      });
+    }
 
     Promise.all([
       messageStore.getPendingConversationKeys(500),