feat: Migrate to MySQL and add unified environment configuration

## Database Migration (SQLite → MySQL)
- Add Alembic migration framework
- Add 'tr_' prefix to all tables to avoid conflicts in shared database
- Remove SQLite support, use MySQL exclusively
- Add pymysql driver dependency
- Change ad_token column to Text type for long JWT tokens

## Unified Environment Configuration
- Centralize all hardcoded settings to environment variables
- Backend: Extend Settings class in app/core/config.py
- Frontend: Use Vite environment variables (import.meta.env)
- Docker: Move credentials to environment variables
- Update .env.example files with comprehensive documentation

## Test Organization
- Move root-level test files to tests/ directory:
  - test_chat_room.py → tests/test_chat_room.py
  - test_websocket.py → tests/test_websocket.py
  - test_realtime_implementation.py → tests/test_realtime_implementation.py
- Fix path references in test_realtime_implementation.py

Breaking Changes:
- CORS now requires explicit origins (no more wildcard)
- All database tables renamed with 'tr_' prefix
- SQLite no longer supported

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

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

app/modules/file_storage/models.py

@@ -8,13 +8,13 @@ from app.core.database import Base
 class RoomFile(Base):
     """File uploaded to an incident room"""
 
-    __tablename__ = "room_files"
+    __tablename__ = "tr_room_files"
 
     # Primary key
     file_id = Column(String(36), primary_key=True)
 
     # Foreign key to incident room (CASCADE delete when room is permanently deleted)
-    room_id = Column(String(36), ForeignKey("incident_rooms.room_id", ondelete="CASCADE"), nullable=False)
+    room_id = Column(String(36), ForeignKey("tr_incident_rooms.room_id", ondelete="CASCADE"), nullable=False)
 
     # File metadata
     uploader_id = Column(String(255), nullable=False)
@@ -36,8 +36,8 @@ class RoomFile(Base):
 
     # Indexes
     __table_args__ = (
-        Index("ix_room_files", "room_id", "uploaded_at"),
-        Index("ix_file_uploader", "uploader_id"),
+        Index("ix_tr_room_files_room_uploaded", "room_id", "uploaded_at"),
+        Index("ix_tr_room_files_uploader", "uploader_id"),
     )
 
     def __repr__(self):