fix: harden get_issue parsing and surface real errors (#27); align CI image publish

get_issue raised 'NoneType' object is not iterable on issues whose
labels/assignees Gitea returns as null or with non-dict elements (the #13
class), which reached clients as an opaque JSON-RPC -32603 with no detail.

- read_tools: skip non-dict label/assignee entries in get_issue_tool
- server: detect a wrapped GiteaNotFoundError via the __cause__ chain and
  return 404 / JSON-RPC -32000 with a clear message; include the exception
  type name in masked internal errors so future masked failures are
  diagnosable without exposing messages or stack traces
- tests: cover non-dict collection elements and the not-found / typed-error
  responses
- ci: rewrite docker.yml to build, smoke-test and push the image to the
  Gitea container registry on merge to main/dev, matching the hiddenden.cafe
  pattern (only REGISTRY_TOKEN required)

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

src/aegis_gitea_mcp/tools/read_tools.py

@@ -295,8 +295,16 @@ async def get_issue_tool(gitea: GiteaClient, arguments: dict[str, Any]) -> dict[
             "body": limit_text(str(issue.get("body", ""))),
             "state": issue.get("state", ""),
             "author": (issue.get("user") or {}).get("login", ""),
-            "labels": [label.get("name", "") for label in (issue.get("labels") or [])],
-            "assignees": [assignee.get("login", "") for assignee in (issue.get("assignees") or [])],
+            "labels": [
+                label.get("name", "")
+                for label in (issue.get("labels") or [])
+                if isinstance(label, dict)
+            ],
+            "assignees": [
+                assignee.get("login", "")
+                for assignee in (issue.get("assignees") or [])
+                if isinstance(assignee, dict)
+            ],
             "created_at": issue.get("created_at", ""),
             "updated_at": issue.get("updated_at", ""),
             "url": issue.get("html_url", ""),