docs(gitea): add guard against direct GiteaMCP calls in description

## Why
Without this guard, the agent could bypass the skill and call Gitea MCP
tools directly, skipping owner/repo resolution and label-ID normalization.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/bin/skills/gitea/SKILL.md

@@ -3,7 +3,8 @@ name: gitea
 description: >
   Use when the user wants to interact with Gitea — create or update issues,
   open or merge pull requests, manage labels and milestones, list branches,
-  or check repo status. Triggers on: "create an issue", "open a PR", "what's
+  or check repo status. Always use this skill to interact with the GiteaMCP, never use GiteaMCP directly.
+  Triggers on: "create an issue", "open a PR", "what's
   open", "label this issue", "create a milestone", "merge the PR", "list
   branches", "close this issue" — even when the user doesn't say "Gitea"
   explicitly. Owner and repo are derived automatically from the git remote;