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

wrangler.jsonc

@@ -25,6 +25,12 @@
 			"id": "a471e264837d4f51b077e078022f0cf0"
 		},
 	],
+	"r2_buckets": [
+		{
+			"binding": "PAYLOAD",
+			"bucket_name": "webhooker-payloads",
+		}
+	],
 	"d1_databases": [
 		{
 			"binding": "DB",