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>

alembic/env.py

@@ -0,0 +1,122 @@
+"""Alembic migrations environment configuration
+
+This configures Alembic to use the application's database settings
+and SQLAlchemy models for migration autogeneration.
+
+All tables use 'tr_' prefix to avoid conflicts in shared database.
+"""
+from logging.config import fileConfig
+import os
+import sys
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+
+# Add parent directory to path so we can import app modules
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+# Import settings and models
+from app.core.config import get_settings
+from app.core.database import Base
+
+# Import all models to register them with Base.metadata
+from app.modules.auth.models import UserSession, User
+from app.modules.chat_room.models import IncidentRoom, RoomMember, RoomTemplate
+from app.modules.realtime.models import Message, MessageReaction, MessageEditHistory
+from app.modules.file_storage.models import RoomFile
+from app.modules.report_generation.models import GeneratedReport
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Load database URL from settings
+settings = get_settings()
+config.set_main_option("sqlalchemy.url", settings.DATABASE_URL)
+
+# Custom version table name with tr_ prefix to avoid conflicts
+VERSION_TABLE = "tr_alembic_version"
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+target_metadata = Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def include_object(object, name, type_, reflected, compare_to):
+    """Filter to only include tables with 'tr_' prefix
+
+    This ensures migrations only affect Task Reporter tables
+    in the shared database.
+    """
+    if type_ == "table":
+        return name.startswith("tr_")
+    return True
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+        include_object=include_object,
+        version_table=VERSION_TABLE,
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata,
+            include_object=include_object,
+            version_table=VERSION_TABLE,
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()