refactor: drop server_sessions table

Add migration to remove server consultation sessions table.
Update schema.sql to remove table definition.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/012_drop_server_sessions.sql

@@ -0,0 +1,5 @@
+-- Drop server consultation sessions table
+-- This table was used for server recommendation consultation feature which is now removed
+
+DROP TABLE IF EXISTS server_sessions;
+DROP INDEX IF EXISTS idx_server_sessions_expires;

schema.sql

@@ -86,18 +86,6 @@ CREATE TABLE IF NOT EXISTS deposit_transactions (
   FOREIGN KEY (user_id) REFERENCES users(id)
 );
 
--- 서버 상담 세션 테이블
-CREATE TABLE IF NOT EXISTS server_sessions (
-  user_id TEXT PRIMARY KEY,
-  status TEXT NOT NULL CHECK(status IN ('gathering', 'recommending', 'selecting', 'ordering', 'completed')),
-  collected_info TEXT,
-  last_recommendation TEXT,
-  messages TEXT,
-  created_at INTEGER NOT NULL,
-  updated_at INTEGER NOT NULL,
-  expires_at INTEGER NOT NULL
-);
-
 -- 서버 주문 테이블
 CREATE TABLE IF NOT EXISTS server_orders (
   id INTEGER PRIMARY KEY AUTOINCREMENT,
@@ -153,7 +141,6 @@ CREATE INDEX IF NOT EXISTS idx_buffer_chat ON message_buffer(user_id, chat_id);
 CREATE INDEX IF NOT EXISTS idx_summary_user ON summaries(user_id, chat_id);
 CREATE INDEX IF NOT EXISTS idx_summary_latest ON summaries(user_id, chat_id, generation DESC);
 CREATE INDEX IF NOT EXISTS idx_users_telegram ON users(telegram_id);
-CREATE INDEX IF NOT EXISTS idx_server_sessions_expires ON server_sessions(expires_at);
 CREATE INDEX IF NOT EXISTS idx_server_orders_user ON server_orders(user_id);
 CREATE INDEX IF NOT EXISTS idx_server_orders_status ON server_orders(status);
 CREATE INDEX IF NOT EXISTS idx_server_orders_idempotency ON server_orders(idempotency_key) WHERE idempotency_key IS NOT NULL;