Enforce repository boundary: Remove DbDep from routers

This commit enforces the repository boundary by eliminating direct database connection
dependencies (DbDep) from all routers. Routers now depend on service context dependencies
that combine the database connection with the related repositories.

Changes:
- Add 5 service context dependencies in dependencies.py:
  * SessionServiceContext: db + session_repo
  * BlocklistServiceContext: db + blocklist_repo + import_log_repo + settings_repo
  * SettingsServiceContext: db + settings_repo
  * BanServiceContext: db + fail2ban_db_repo
  * HistoryServiceContext: db + fail2ban_db_repo + history_archive_repo

- Refactor all 9 routers (auth, bans, blocklist, config_misc, dashboard, geo,
  history, jails, setup) to use service contexts instead of DbDep.

- Update Backend-Development.md with clear examples of the new pattern and
  documentation of available service contexts.

Rationale:
- Enforces the repository boundary through the dependency system
- Makes database operations explicit and auditable
- Improves testability by allowing service contexts to be mocked
- Prevents accidental direct database access from routers

The deprecated DbDep remains available for backward compatibility with
services that have not yet been refactored, but routers can no longer import it.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/routers/setup.py

@@ -10,7 +10,7 @@ from __future__ import annotations
 import structlog
 from fastapi import APIRouter, HTTPException, status
 
-from app.dependencies import AppDep, DbDep, SettingsDep
+from app.dependencies import AppDep, SettingsDep, SettingsServiceContextDep
 from app.models.setup import SetupRequest, SetupResponse, SetupStatusResponse, SetupTimezoneResponse
 from app.services import setup_service
 from app.utils.runtime_state import update_app_settings
@@ -46,14 +46,14 @@ async def get_setup_status(app: AppDep) -> SetupStatusResponse:
 async def post_setup(
     app: AppDep,
     body: SetupRequest,
-    db: DbDep,
+    settings_ctx: SettingsServiceContextDep,
 ) -> SetupResponse:
     """Persist the initial BanGUI configuration.
 
     Args:
         app: The FastAPI application instance.
         body: Setup request payload validated by Pydantic.
-        db: Injected aiosqlite connection.
+        settings_ctx: Settings service context containing db and repository.
 
     Returns:
         :class:`~app.models.setup.SetupResponse` on success.
@@ -61,14 +61,14 @@ async def post_setup(
     Raises:
         HTTPException: 409 if setup has already been completed.
     """
-    if is_setup_complete_cached(app) or await setup_service.is_setup_complete(db):
+    if is_setup_complete_cached(app) or await setup_service.is_setup_complete(settings_ctx.db):
         raise HTTPException(
             status_code=status.HTTP_409_CONFLICT,
             detail="Setup has already been completed.",
         )
 
     await setup_service.run_setup(
-        db,
+        settings_ctx.db,
         master_password=body.master_password,
         database_path=body.database_path,
         fail2ban_socket=body.fail2ban_socket,