ci(cd): skip docs-only pushes; move HOW_GITEA_MCP_WORKS into docs/

Relocate the doc under docs/ and add paths-ignore: ['docs/**'] to the CD push
trigger so documentation-only changes no longer rebuild the image and roll the
pod. Branch pushes with only docs/ changes are skipped; tag (v*) pushes and any
push touching code still deploy.

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

.gitea/workflows/cd.yml

@@ -4,6 +4,10 @@ name: CD
   push:
     branches: [main]
     tags: ["v*"]
+    # Docs-only pushes don't change the image — skip the build/deploy roll.
+    # (Only applies to branch pushes; tag pushes always trigger.)
+    paths-ignore:
+      - 'docs/**'
 
 env:
   IMAGE: gitea-mcp