refactor(v2): use Chat SDK webhooks proxy and clean up webhook server

Route webhook requests through chat.webhooks[name]() instead of calling
adapter.handleWebhook() directly, getting proper auto-initialization and
signature verification. Extract Node↔Web Request/Response conversion
into reusable helpers, parse URL pathname properly for query string
safety, and support all HTTP methods (not just POST).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db/session-db.ts

@@ -197,7 +197,17 @@ export function insertRecurrence(
   db.prepare(
     `INSERT INTO messages_in (id, seq, kind, timestamp, status, process_after, recurrence, platform_id, channel_type, thread_id, content)
      VALUES (?, ?, ?, datetime('now'), 'pending', ?, ?, ?, ?, ?, ?)`,
-  ).run(newId, nextEvenSeq(db), msg.kind, nextRun, msg.recurrence, msg.platform_id, msg.channel_type, msg.thread_id, msg.content);
+  ).run(
+    newId,
+    nextEvenSeq(db),
+    msg.kind,
+    nextRun,
+    msg.recurrence,
+    msg.platform_id,
+    msg.channel_type,
+    msg.thread_id,
+    msg.content,
+  );
 }
 
 export function clearRecurrence(db: Database.Database, messageId: string): void {