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

migrations/0008_storage_d1.sql

@@ -0,0 +1,25 @@
+-- D1 tables replacing ephemeral high-frequency KV keys (dedup, delivery state,
+-- message tracking). Keeps KV for things that still benefit from key-based
+-- access with short TTL; these tables relieve the KV write quota.
+
+CREATE TABLE IF NOT EXISTS dedup_keys (
+  key TEXT PRIMARY KEY,
+  claimed_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL
+);
+CREATE INDEX IF NOT EXISTS idx_dedup_keys_expires_at ON dedup_keys (expires_at);
+
+CREATE TABLE IF NOT EXISTS delivery_state (
+  key TEXT PRIMARY KEY,
+  status TEXT NOT NULL,
+  updated_at INTEGER NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS message_tracking (
+  event_id TEXT NOT NULL,
+  target_id TEXT NOT NULL,
+  message_id TEXT NOT NULL,
+  updated_at INTEGER NOT NULL,
+  PRIMARY KEY (event_id, target_id)
+);
+CREATE INDEX IF NOT EXISTS idx_message_tracking_updated_at ON message_tracking (updated_at);