refactor: organize API routers and services into subpackages

Service organization (19 files moved into 6 subpackages):
- services/instance/ — event_bus, health_monitor, lifecycle_hooks
- services/config/ — config_profile_resolver
- services/git/ — clone, git_operations, git_service
- services/build/ — docker_build, manifest_compiler
- services/terminal/ — terminal_manager, terminal_session
- services/shared/ — correlation, file_service, notification_service,
  permission_fixer, readiness_probe, ssh_keys, tunnel, workspace_manager

API router organization (16 files moved into 6 subpackages):
- api/tool/ — tool_instances, tool_types, tool_definitions,
  tool_types_validation, sessions (extracted from tool_instances)
- api/config/ — config_profiles, user_config
- api/workspace/ — workspaces, workspace_files, workspace_git,
  workspace_instances
- api/user/ — users, auth, ssh_keys
- api/project/ — projects, git_repositories
- api/system/ — health, events, notifications, dashboard, terminal,
  instance_proxy

Updated main.py imports and all __init__.py re-exports.
Sessions router extracted from tool_instances.py into api/tool/sessions.py.

Quality gates: py_compile passed, ruff passed.

apps/api/src/main.py

@@ -7,27 +7,30 @@ from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
 
-from src.api.auth import router as auth_router
-from src.api.dashboard import router as dashboard_router
-from src.api.events import router as events_router
-from src.api.git_repositories import router as git_repositories_router
-from src.api.health import router as health_router
-from src.api.projects import router as projects_router
-from src.api.ssh_keys import router as ssh_keys_router
-from src.api.terminal import router as terminal_router
-from src.api.instance_proxy import router as instance_proxy_router
-from src.api.config_profiles import router as config_profiles_router
-from src.api.tool_definitions import router as tool_definitions_router
-from src.api.tool_instances import router as tool_instances_router
-from src.api.tool_instances import sessions_router
-from src.api.tool_types import router as tool_types_router
-from src.api.notifications import router as notifications_router
-from src.api.user_config import router as user_config_router
-from src.api.users import router as users_router
-from src.api.workspace_files import router as workspace_files_router
-from src.api.workspace_git import router as workspace_git_router
-from src.api.workspace_instances import router as workspace_instances_router
-from src.api.workspaces import all_workspaces_router, router as workspaces_router
+from src.api.config import config_profiles_router, user_config_router
+from src.api.project import git_repositories_router, projects_router
+from src.api.system import (
+    dashboard_router,
+    events_router,
+    health_router,
+    instance_proxy_router,
+    notifications_router,
+    terminal_router,
+)
+from src.api.tool import (
+    sessions_router,
+    tool_definitions_router,
+    tool_instances_router,
+    tool_types_router,
+)
+from src.api.user import auth_router, ssh_keys_router, users_router
+from src.api.workspace import (
+    all_workspaces_router,
+    workspace_files_router,
+    workspace_git_router,
+    workspace_instances_router,
+    workspaces_router,
+)
 from src.config import Settings
 from src.models import Notification  # noqa: F401 – Alembic model discovery
 from src.models import TerminalSessionModel  # noqa: F401 – Alembic model discovery