feat(pii): NER tier engine — privacy-filter.cpp backend + NER-centric PII filter (#10360)

Squashed feat/pii-ner-tier-engine rebased onto master (was 45 commits; see
backup/pii-ner-tier-engine-prerebase). Net change:

- privacy-filter.cpp: standalone GGML engine for the openai-privacy-filter
  PII/NER token classifier, wired as a LocalAI gRPC backend (CPU/CUDA/Vulkan).
  TokenClassify moves off the patched llama.cpp path onto this backend.
- PII filter reworked to be NER-centric (encoder/NER detection tier scanning
  whole conversations as one document), with a recreated bounded restricted-
  regex secret-matching pattern detector tier alongside it (per-model
  pii_detection.builtins / .patterns + core/services/routing/piipattern).
- Detection labelled by source (ner vs pattern); backend trace / confidence /
  debug observability; analyze/redact exposed as a synchronous API.
- Instance-wide default detector policy + per-usecase default-on; request
  filtering extended to completions, embeddings, edits & Ollama.
- React UI: NER-centric PII editor, detector-models table, pattern/builtins
  editor, middleware default-policy UI.
- Gallery: privacy-filter-multilingual token-classify model + NER install
  filter; token_classify known_usecase; batch sized to context for NER models.
  privacy-filter backend registered in the backend gallery (cpu/vulkan/cuda-13
  meta + image entries with a capabilities map) matching its CI matrix jobs,
  and an /import-model auto-detect importer (PrivacyFilterImporter, narrow
  privacy-filter GGUF detection) replacing the prior pref-only registration.

Reconciled against master's independent evolution:

- Dropped master's PIIPatternOverrides feature (global-pattern runtime
  overrides + /api/pii/patterns API + runtime_settings.json persistence). The
  per-model NER + pattern-detector design supersedes it; it was built on the
  global redactor pattern set this branch replaced.
- Reverted the llama.cpp Score carry-patch (0006-server-task-type-score):
  removed the patch and restored master's grpc-server.cpp Score RPC (direct
  llama_decode, slot-loop bypass) and LLAMA_VERSION pin, plus master's
  model_config validation forbidding score + chat/completion/embeddings on
  llama-cpp. token_classify is unaffected (it runs on the privacy-filter
  backend, not llama-cpp).

Assisted-by: Claude:claude-opus-4-8 [Claude Code]

Signed-off-by: Richard Palethorpe <io@richiejp.com>

core/trace/backend_trace.go

@@ -34,6 +34,8 @@ const (
 	BackendTraceAudioTransform  BackendTraceType = "audio_transform"
 	BackendTraceModelLoad       BackendTraceType = "model_load"
 	BackendTraceScore           BackendTraceType = "score"
+	BackendTraceTokenClassify   BackendTraceType = "token_classify"
+	BackendTracePatternPII      BackendTraceType = "pattern_pii"
 	BackendTraceVectorStore     BackendTraceType = "vector_store"
 )
 
@@ -59,10 +61,12 @@ type BackendTrace struct {
 // runaway buffer when a caller streams MB-scale payloads.
 const MaxTraceBodyBytes = 1 << 20
 
-var backendTraceBuffer *circularbuffer.Queue[*BackendTrace]
-var backendMu sync.Mutex
-var backendLogChan = make(chan *BackendTrace, 100)
-var backendInitOnce sync.Once
+var (
+	backendTraceBuffer *circularbuffer.Queue[*BackendTrace]
+	backendMu          sync.Mutex
+	backendLogChan     = make(chan *BackendTrace, 100)
+	backendInitOnce    sync.Once
+)
 
 // backendMaxBodyBytes caps each captured string value in a BackendTrace.Data
 // field to keep the /api/backend-traces JSON small enough for the admin UI to