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/escalation.py

@@ -2,7 +2,7 @@
 
 The escalation ladder is the cheapest-first ordering of extraction tiers:
 
-    fast  ->  structured  ->  ocr   ( ->  llm, reserved)
+    fast  ->  structured  ->  ocr-incluster  ->  ocr-upstream   ( ->  llm, reserved)
 
 It mirrors the ``tier`` vocabulary documented on
 :meth:`DocumentProcessor.tier <.base.DocumentProcessor.tier>` and the