feat(ingest): per-tier escalation via procrastinate queue-hop

Split external (procrastinate) document processing into per-tier queues so a
document is attempted at most once per tier and requeued to the next tier's
queue on a low-quality parse, using procrastinate's native retry.

- escalation.py: TIER_LADDER (fast->structured->ocr) + EscalateError signal
- registry: process_tier (one tier) + evaluate_escalation post-parse gate
  (reuses classify_from_text) + next_available_tier; shared _classify_result
  and _oversize_result with the inline pipeline
- processor: process_document(tier=...) runs one tier and raises EscalateError
  before embed (junk text never indexed); inline memory path unchanged
- queue/procrastinate: ingest-fast|structured|ocr queues; TieredEscalationStrategy
  (queue-hop on EscalateError, bounded same-tier transient retry); queue-aware
  task; producer defers to ingest-fast; per-queue counts + all-queue reclaim
- cli: worker --tier {fast,structured,ocr}
- billing: pages_ocr usage event + pipeline_tier metadata (paid OCR billed apart)
- observability: astrolabe_ingest_queue_depth{queue,status} gauge + per-queue
  counts in nc_get_vector_sync_status / management status endpoint
- config: INGEST_ESCALATION_ENABLED (default true), INGEST_TRANSIENT_MAX_ATTEMPTS

INGEST_ESCALATION_ENABLED=false and INGEST_QUEUE=memory preserve prior behaviour.

Deck #323.

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

nextcloud_mcp_server/models/semantic.py

@@ -193,6 +193,15 @@ class VectorSyncStatusResponse(BaseResponse):
             "queue backend; None on the in-memory backend"
         ),
     )
+    job_counts_by_queue: dict[str, dict[str, int]] | None = Field(
+        default=None,
+        description=(
+            "Per-tier-queue ingest job counts {queue: {status: count}} on the "
+            "postgres backend (Deck #323), so an operator can see whether work is "
+            "backed up on ingest-fast vs waiting on ingest-structured/ingest-ocr; "
+            "None on the in-memory backend"
+        ),
+    )
 
 
 __all__ = [