feat(api): pin response_model on dict-returning mutation routes

Every mutation route that returned an untyped dict now declares
response_model at the decorator. MessageResponse covers the eight
{"message": ...} envelopes (change-password, mutate-decky, mutate-
interval, update-deployment-limit, update-global-mutation-interval,
delete-user, update-user-role, reset-user-password). Purpose-built
models cover the richer shapes (DeployResponse for /deckies/deploy,
PurgeResponse for /config/reinit, ReapReportResponse for /reap-orphans,
UserResponse for /config/users). 204-No-Content and Response/
ORJSONResponse routes stay as-is.

The wire shape for clients is unchanged — the envelopes already only
shipped a message field. What changes is that a handler which
accidentally returns a richer dict (e.g. a full user row including
password_hash) would be silently stripped to the declared fields at
serialization time.

Also flips F4/D "expensive LIKE" to accepted (new DA-09) — the /logs
and /attackers search routes LIKE-scan unbounded columns, but both are
admin-gated, limit-capped, and operator rate-limit scope per DA-04.
FTS5 stays a performance TODO, not a security blocker.

decnet/web/router/config/api_manage_users.py

@@ -8,8 +8,9 @@ from decnet.web.dependencies import require_admin, invalidate_user_cache, repo
 from decnet.web.router.config.api_get_config import invalidate_list_users_cache
 from decnet.web.db.models import (
     CreateUserRequest,
-    UpdateUserRoleRequest,
+    MessageResponse,
     ResetUserPasswordRequest,
+    UpdateUserRoleRequest,
     UserResponse,
 )
 
@@ -19,6 +20,7 @@ router = APIRouter()
 @router.post(
     "/config/users",
     tags=["Configuration"],
+    response_model=UserResponse,
     responses={
         400: {"description": "Bad Request (e.g. malformed JSON)"},
         401: {"description": "Could not validate credentials"},
@@ -56,6 +58,7 @@ async def api_create_user(
 @router.delete(
     "/config/users/{user_uuid}",
     tags=["Configuration"],
+    response_model=MessageResponse,
     responses={
         401: {"description": "Could not validate credentials"},
         403: {"description": "Admin access required / cannot delete self"},
@@ -81,6 +84,7 @@ async def api_delete_user(
 @router.put(
     "/config/users/{user_uuid}/role",
     tags=["Configuration"],
+    response_model=MessageResponse,
     responses={
         400: {"description": "Bad Request (e.g. malformed JSON)"},
         401: {"description": "Could not validate credentials"},
@@ -111,6 +115,7 @@ async def api_update_user_role(
 @router.put(
     "/config/users/{user_uuid}/reset-password",
     tags=["Configuration"],
+    response_model=MessageResponse,
     responses={
         400: {"description": "Bad Request (e.g. malformed JSON)"},
         401: {"description": "Could not validate credentials"},