Add official Gitea MCP server to base image

Install gitea-mcp v1.1.0 (Go binary from gitea.com/gitea/gitea-mcp)
using the same multi-arch pattern as gosu/fzf/bat. Provides 50+ MCP
tools for Gitea API — repos, issues, PRs, releases, branches, wiki,
and Actions.

Disabled by default in auto-generated opencode.json (requires
GITEA_ACCESS_TOKEN and GITEA_HOST to be useful). Users enable it by
setting those env vars in .env and flipping enabled to true in their
opencode.json.

Env vars forwarded into the container via docker-compose.yml and
docker-compose.shared.yml environment blocks. Same {env:VAR} pattern
as the GitHub MCP server.

Docs updated: README.md (new Gitea MCP section with setup steps),
DOCKER_HUB.md (tools list), CHANGELOG.md (v1.14.28b entry).

docker-compose.yml

@@ -33,6 +33,9 @@ services:
       - .env
     environment:
       - TERM=xterm-256color
+      - GITHUB_PERSONAL_ACCESS_TOKEN=${GITHUB_PERSONAL_ACCESS_TOKEN:-}
+      - GITEA_ACCESS_TOKEN=${GITEA_ACCESS_TOKEN:-}
+      - GITEA_HOST=${GITEA_HOST:-}
     volumes:
       # Host workspace — mount your project here
       - ${WORKSPACE_PATH:-.}:/workspace