fix(backends): flag a llama-cpp backend that predates native decisions (#12733)

A decision request (/v1/systemone, /v1/decisions) sends Score with
question_type "systemone". A backend built before native decisions ignores
that field and runs plain scoring, so the caller saw "Score was not enabled"
(500) or "candidates must be non-empty" (400). The gallery "latest" image can
lag behind the server, and the upgrade check compares only tag, version and
digest, so /backends/upgrades did not list the backend.

Recognise those two errors for a decision request, return 501 with a message
that says the backend is older than the server and must be upgraded, and mark
the backend stale. The upgrade check now reports a marked backend with a
`reason`, and refreshes at once. Reinstalling the backend drops the mark; if
the new image is still old, the next request marks it again. Model loading is
not affected.

Refreshing the "latest" backend image is a separate publishing step and is
not part of this change.

Refs #12693

Assisted-by: Claude Code:claude-sonnet-5-5 [go vet] [go test]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

docs/content/features/decisions.md

@@ -290,6 +290,15 @@ accept 2–10 levels; this backend-specific limit does not constrain vllm-cpp.
 Older forks without native decision support return 501. Missing decision metadata
 also returns 501, while backend invalid requests return 400.
 
+A `llama-cpp` backend image built before native decisions cannot answer these
+requests, even when the gallery reports it as up to date. LocalAI detects this
+from the failed request: it returns 501 with a message that the backend is older
+than the server, and `GET /backends/upgrades` lists the backend with a `reason`
+field. Upgrade the backend, or install a current build such as the
+`-development` variant. Adding `score` to `known_usecases` does not help. The
+flag clears when the backend is reinstalled; if the reinstalled image is still
+old, the next decision request flags it again.
+
 ### Bounded image input
 
 The public routes and internal decision validator share an image contract. Supply