feat(storage): migrate config, dedup and delivery state to D1

- Move oversized queue payloads from KV to R2 (PAYLOAD binding, webhooks/YYYY/MM/DD/*.json, KV queue:payload:* fallback)
- Persist routes/groups to D1 (d1_routes/d1_groups) with memory -> KV -> D1 three-tier cache, seeded from legacy KV config keys
- Move webhook dedup (dedup_keys), delivery state (delivery_state) and message tracking (message_tracking) to D1 via canUseD1 probe with automatic KV fallback
- Batch send_logs inserts (recordSendBatch) and add group_id/ts index
- Add storage-prune scheduled task for expired dedup/state/tracking rows
- Add TTL to invite:group:{id} index and audit all ephemeral KV keys
- Add D1 indexes for the new tables
- Sync AGENTS.md, README.md/zh and docs/ (en/zh) with the new storage layout

docs/guide/faq.md

@@ -34,4 +34,4 @@ No — the worker requires the KV and D1 bindings declared in `wrangler.jsonc` a
 
 ## Where is data stored?
 
-Configuration lives in Cloudflare KV (`config:routes`, `config:groups`); send/audit logs and platform↔GitHub links live in D1. See [Storage Layout](./storage#kv-storage-layout).
+Configuration lives in D1 (`d1_routes`/`d1_groups`, with KV as a cache); webhook dedup, delivery state and message-update tracking also live in D1 with KV fallback; send/audit logs and platform↔GitHub links live in D1. R2 optionally parks oversized payloads. See [Storage Layout](./storage#storage-decisions).