[P1] Scale shard processing and bound hot-path concurrency

[apple050620312]

Summary

• Add validated SHARD_COUNT and SHARD_IDS configuration for distributed shard workers.
• Move synchronous database operations off the event loop with bounded execution time.
• Add bounded TTL/LRU caches for guild settings, filters, and webhooks.
• Bound link-fix and EmbedEZ concurrency and rate-limit overload warnings.
• Replace analytics row loading with database-side counts and buffered asynchronous event writes.
• Document multi-process shard assignment and capacity-tuning controls.

Priority

P1 — removes event-loop and upstream-service bottlenecks that become critical at roughly 50,000 guilds.

Validation

• Independent shard parsing and bounded-cache smoke checks pass.
• Runtime imports and all Python AST parsing checks pass.