feat(worker): structured logs + metrics + traces for ingest worker

The external split-worker ingest pods (MCP_ROLE=worker / procrastinate) had
no observability: the worker CLI entrypoint never started a Prometheus
metrics server and never configured structured logging, so the pods that do
the real parse/embed/upsert work were invisible to Prometheus and emitted
plain-text logs the platform pipeline couldn't parse.

The always-on API pod bootstraps observability in its lifespan (app.py), but
the worker has its own entrypoint and never went through that path (or
uvicorn's JSON log_config). Add `_init_worker_observability()` mirroring the
API pod: setup_logging (JSON), setup_metrics on METRICS_PORT when
METRICS_ENABLED, and setup_tracing when an OTLP endpoint is configured.
Runs after the INGEST_QUEUE=postgres check so a misconfigured worker fails
fast without binding a metrics port.

This also unblocks the document-pipeline observability shipped in #831
(Deck #175): the astrolabe_* parse/embed/chunk metrics and the
document_processor.parse span are recorded in the shared registry/processor
code the worker executes — they were simply never exposed in external mode
because the worker served no /metrics and set up no tracer.

Deck #310, unblocks #175.

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

nextcloud_mcp_server/cli.py

@@ -6,6 +6,7 @@ import click
 import uvicorn
 
 from nextcloud_mcp_server.config import (
+    Settings,
     get_database_url,
     get_settings,
     is_ephemeral_token_db,
@@ -17,7 +18,12 @@ from nextcloud_mcp_server.migrations import (
     show_migration_history,
     upgrade_database,
 )
-from nextcloud_mcp_server.observability import get_uvicorn_logging_config
+from nextcloud_mcp_server.observability import (
+    get_uvicorn_logging_config,
+    setup_logging,
+    setup_metrics,
+    setup_tracing,
+)
 from nextcloud_mcp_server.server import AVAILABLE_APPS
 
 from .app import get_app
@@ -284,6 +290,44 @@ def run(
     )
 
 
+def _init_worker_observability(settings: Settings) -> None:
+    """Configure logging, metrics, and tracing for the ingest worker.
+
+    Mirrors the observability bootstrap the API pod performs in its lifespan
+    (``app.py``), but for the standalone ``worker`` entrypoint which never runs
+    uvicorn. Without this the worker emits plain-text logs and serves no
+    ``/metrics`` endpoint, so the astrolabe_* document-pipeline metrics and the
+    ``document_processor.parse`` spans (recorded in the shared registry/processor
+    code the worker executes) stay invisible in external split-worker mode
+    (Deck #310 / #175).
+    """
+    # Structured logging first, so every subsequent startup line is JSON like
+    # the API's — the worker entrypoint never went through uvicorn's log_config.
+    setup_logging(
+        log_format=settings.log_format,
+        log_level=settings.log_level,
+        include_trace_context=settings.log_include_trace_context,
+    )
+
+    if settings.metrics_enabled:
+        setup_metrics(port=settings.metrics_port)
+        logger.info(
+            "Prometheus metrics enabled on dedicated port %s", settings.metrics_port
+        )
+
+    if settings.otel_exporter_otlp_endpoint:
+        setup_tracing(
+            service_name=settings.otel_service_name,
+            otlp_endpoint=settings.otel_exporter_otlp_endpoint,
+            otlp_verify_ssl=settings.otel_exporter_verify_ssl,
+            sampling_rate=settings.otel_traces_sampler_arg,
+        )
+        logger.info(
+            "OpenTelemetry tracing enabled (endpoint: %s)",
+            settings.otel_exporter_otlp_endpoint,
+        )
+
+
 @click.command()
 @click.option(
     "--concurrency",
@@ -319,6 +363,15 @@ def worker(concurrency: int | None):
             f"resolved INGEST_QUEUE={settings.ingest_queue!r}"
         )
 
+    # Initialize observability once the config is known to be runnable. The
+    # always-on API pod does this in its lifespan (app.py); the worker has its
+    # own entrypoint, so without this it emits plain-text logs and exposes no
+    # /metrics — leaving the ingest workload (which does the real
+    # parse/embed/upsert work, and where the astrolabe_* pipeline metrics +
+    # document_processor.parse spans are recorded) invisible in external
+    # split-worker mode (Deck #310, unblocks #175).
+    _init_worker_observability(settings)
+
     from nextcloud_mcp_server.vector.queue.procrastinate import (  # noqa: PLC0415
         INGEST_QUEUE_NAME,
         apply_ingest_queue_schema,