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/shared/config/index.ts

@@ -197,6 +197,7 @@ export const configSchema = z
       .positive()
       .default(1024),
     AI_LLM_TEXT_BATCH_SIZE: z.coerce.number().int().positive().default(60),
+    AI_LLM_MAX_COMPLETION_TOKENS: z.coerce.number().int().positive().default(16384),
     AI_LLM_MEDIA_ANALYSIS_TIMEOUT_MS: z.coerce
       .number()
       .int()