feat: tool definition manifest system (PR 1)

- Add ToolDefinitionManifest model with base image versioning
- Add manifest compiler: Dockerfile + Compose generation from JSON manifests
- Add permission fixer: post-start chown/chmod for mount policies
- Add tool definition CRUD API with live compile preview endpoint
- Integrate manifest-based startup flow in start_instance
- Add Alembic migration with data conversion for pi-agent
- Add 48 unit tests for manifest compiler, permission fixer, docker service
- Keep backward compatibility with legacy dockerfile_template/compose_template

Migration: applied successfully. Pi-agent converted to manifest.
Quality gates: pytest (146 passed, 4 pre-existing unrelated failures)

apps/api/src/models/__init__.py

@@ -4,9 +4,23 @@ from src.models.config_profile import ConfigProfile, ConfigProfileInclude
 from src.models.git_repository import GitRepository
 from src.models.project import Project
 from src.models.ssh_key import SSHKey
+from src.models.tool_definition_manifest import ToolDefinitionManifest
 from src.models.tool_instance import ToolInstance
 from src.models.tool_type import ToolType
 from src.models.user import User
 from src.models.user_config import UserConfig
 
-__all__ = ["Base", "ConfigFolder", "ConfigProfile", "ConfigProfileInclude", "GitRepository", "Project", "SSHKey", "ToolInstance", "ToolType", "User", "UserConfig"]
+__all__ = [
+    "Base",
+    "ConfigFolder",
+    "ConfigProfile",
+    "ConfigProfileInclude",
+    "GitRepository",
+    "Project",
+    "SSHKey",
+    "ToolDefinitionManifest",
+    "ToolInstance",
+    "ToolType",
+    "User",
+    "UserConfig",
+]