Merge branch 'feat/tool-definition-manifest' into dev

Conflicts resolved:
- models/__init__.py: kept both TerminalSessionModel (from dev) and
  ToolDefinitionManifest (from feature branch)
- alembic migration: kept full migration (already applied to DB)
- openspec/config.yaml: kept full config with SDD settings

apps/api/src/main.py

@@ -25,6 +25,7 @@ from src.api.tool_types import router as tool_types_router
 from src.api.user_config import router as user_config_router
 from src.api.users import router as users_router
 from src.config import Settings
+from src.models.terminal_session import TerminalSessionModel  # noqa: F401 – Alembic model discovery
 from src.database import init_database
 from src.logging_config import (
     ExceptionLoggingMiddleware,