docs(config): clarify DOCLING_SERVE_URL default is compose-only (#134)

The default value 'http://docling-serve:5001' only resolves inside
the docker-compose dev stack (where 'docling-serve' is the service
name). An operator deploying anywhere else — Kubernetes, ECS without
the bundled compose file, a single VM, anything — sees the default,
nothing complains at startup, and every document submission silently
fails when the api can't connect.

Expand the Field description to say so plainly: it's required, there
is no in-process fallback, and these are the two address shapes
operators actually use:

  http://localhost:5001     — sidecar in the same task / pod
  http://<dns-or-host>:5001 — separate docling-serve service

No behaviour change. Docstring-only.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bbertucc

src/config.py

@@ -155,7 +155,16 @@ class Settings(BaseSettings):
     # Docling-serve sidecar configuration
     docling_serve_url: str = Field(
         default="http://docling-serve:5001",
-        description="Base URL of the docling-serve sidecar",
+        description=(
+            "Base URL of the docling-serve service. **Required** — every "
+            "document submission calls this; there is no in-process docling "
+            "fallback. The default 'http://docling-serve:5001' resolves only "
+            "inside the docker-compose dev stack, where 'docling-serve' is "
+            "the compose service name. For any other deployment set this to "
+            "the actual address: 'http://localhost:5001' when docling-serve "
+            "runs as a sidecar in the same task/pod, or the full "
+            "DNS/hostname of a separate docling-serve service otherwise."
+        ),
     )
     docling_serve_timeout: float = Field(
         ge=10.0,