fix: Add missing meeting_number column to table definitions

The meetings router was using meeting_number column but it was
not defined in the MYSQL_TABLES and SQLITE_TABLES schema definitions,
causing HTTP 500 errors when creating meetings.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/database.py

@@ -209,6 +209,7 @@ MYSQL_TABLES = [
     CREATE TABLE IF NOT EXISTS meeting_records (
         meeting_id INT PRIMARY KEY AUTO_INCREMENT,
         uuid VARCHAR(64) UNIQUE,
+        meeting_number VARCHAR(20),
         subject VARCHAR(200) NOT NULL,
         meeting_time DATETIME NOT NULL,
         location VARCHAR(100),
@@ -257,6 +258,7 @@ SQLITE_TABLES = [
     CREATE TABLE IF NOT EXISTS meeting_records (
         meeting_id INTEGER PRIMARY KEY AUTOINCREMENT,
         uuid TEXT UNIQUE,
+        meeting_number TEXT,
         subject TEXT NOT NULL,
         meeting_time DATETIME NOT NULL,
         location TEXT,