docs(compose): keep the prod comment block's sentences with their own variable (#281)

ANTHROPIC_API_KEY's explanatory paragraph already had a dangling continuation trailing after later entries. When REMBG_URL was added, its entry was inserted ahead of that continuation, so the file read as though "put a spend limit on the key in the Anthropic console" belonged to the background-removal sidecar rather than to Anthropic. This file is read during the cutover runbook, so a misattributed sentence there is not just cosmetic.

Reordered the comment lines so ANTHROPIC_API_KEY's full paragraph is contiguous and REMBG_URL's own two-line entry stands on its own at the end. No environment: line was touched — only the comment block above the services: section.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docker-compose.prod.yml

@@ -92,6 +92,12 @@
 #                         failing, so an empty value is a working configuration.
 #   ANTHROPIC_API_KEY     Optional. Drafts a listing from a submitted photo
 #                         (#223). Unset means submissions still arrive and wait
+#                         undrafted, which is a working configuration for the
+#                         same reason USPS is. The one credential here that
+#                         spends money per call, and on a path anybody holding
+#                         an upload link can trigger — put a spend limit on the
+#                         key in the Anthropic console, because nothing in this
+#                         repository can enforce one.
 #   ANTHROPIC_WORKSPACE_ID  Required alongside the key above when that key is
 #                         identity-linked. Without it every draft fails with a
 #                         400 naming the missing header (#271).
@@ -100,12 +106,6 @@
 #                         still sends and carries no shortcuts.
 #   REMBG_URL             Optional. The background-removal sidecar, e.g.
 #                         http://rembg-syn:7000. Unset turns the feature off.
-#                         undrafted, which is a working configuration for the
-#                         same reason USPS is. The one credential here that
-#                         spends money per call, and on a path anybody holding
-#                         an upload link can trigger — put a spend limit on the
-#                         key in the Anthropic console, because nothing in this
-#                         repository can enforce one.
 #
 # The names above are what this file reads. A stack variable under any other
 # name is substituted nowhere and never reaches the container, so reconciling