fix(ingest): address review round 1 (Literal kind + log tidy)

- escalation: EscalationDecision.kind is now Literal["hop","suppressed"] so ty
  catches a bad kind statically (and the processor branch is exhaustive).
- processor: simplify the suppressed-escalation log line (no longer repeats
  to_tier / tier).
- registry: clarify _tier_available's ignore_enabled drops the OCR-enabled gate
  specifically (a future per-tier gate would extend the condition).

Deck #324.

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

nextcloud_mcp_server/document_processors/escalation.py

@@ -22,6 +22,7 @@ mapping lives in the queue layer, which imports :class:`EscalateError` from here
 from __future__ import annotations
 
 from dataclasses import dataclass
+from typing import Literal
 
 # Cheapest-first. ``llm`` is reserved (see base.DocumentProcessor.tier) and not
 # wired yet, so it is intentionally absent from the live ladder.
@@ -46,7 +47,7 @@ class EscalationDecision:
     exists at all (no processor registered for it).
     """
 
-    kind: str  # "hop" | "suppressed"
+    kind: Literal["hop", "suppressed"]
     to_tier: str
     reason: str  # empty_text | low_confidence