fix(ingest): suppress misleading batch-fallback warn for in-cluster rung

Address claude-review round 3 on #922:

- Important: _process_batch emitted "no gateway backend (provider=mistral or
  EMBEDDING_GATEWAY_URL unset)" for the gateway_only in-cluster rung, where the
  gateway IS configured — sending operators chasing a non-existent config
  problem. The real reason is "in-cluster GPU is synchronous-only; batch is the
  upstream path". Guard the warning with `if not self._gateway_only`. Extended
  test_gateway_only_processor_never_uses_batch_mode to drive _process_batch and
  assert _batch_fallback_warned stays False.
- Nits: refresh stale ladder in escalation.py module docstring
  (fast->structured->ocr-incluster->ocr-upstream); fix "minimum='ocr'" ->
  "ocr-incluster" in a test docstring; rename stale tier="ocr" ->
  "ocr-upstream" in test_process_tier_oversize_fails_fast.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/document_processors/ocr.py

@@ -499,10 +499,15 @@ class OcrProcessor(DocumentProcessor):
             return None
         client = await self._get_batch_client()
         if client is None:
-            self._batch_fallback(
-                "no gateway backend (provider=mistral or EMBEDDING_GATEWAY_URL unset)",
-                filename,
-            )
+            # The in-cluster (gateway_only) rung returns None here BY DESIGN — the
+            # GPU is synchronous-only, batch is the upstream Mistral path — so don't
+            # emit the "no gateway backend" warning (the gateway IS configured; that
+            # warning would send an operator chasing a non-existent config problem).
+            if not self._gateway_only:
+                self._batch_fallback(
+                    "no gateway backend (provider=mistral or EMBEDDING_GATEWAY_URL unset)",
+                    filename,
+                )
             return None
 
         # Lazy import: keep the vector/DB stack off the document_processors load