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/db/models/deploy.py

@@ -17,3 +17,13 @@ class DeployIniRequest(BaseModel):
     # This field now enforces strict INI structure during Pydantic initialization.
     # The OpenAPI schema correctly shows it as a required string.
     ini_content: IniContent = PydanticField(..., description="A valid INI formatted string")
+
+
+class DeployResponse(BaseModel):
+    message: str
+    mode: str
+
+
+class PurgeResponse(BaseModel):
+    message: str
+    deleted: dict[str, int]