feat: rename to gitea-mcp-extended and add package publishing workflows

Rename the fork from gitea-mcp to gitea-mcp-extended to reflect the
significantly expanded tool coverage (299 vs upstream's 93 tools).

- Rename Go module path and all import references
- Rename binary to gitea-mcp-extended in Makefile, Dockerfile, .gitignore
- Point .goreleaser.yaml gitea_urls to git.lethalbits.com
- Replace release-tag workflow with goreleaser + Generic Package Registry publishing
- Replace release-nightly workflow with cross-platform build + nightly package publishing
- Update CLAUDE.md project description and tool count

.goreleaser.yaml

@@ -71,6 +71,6 @@ release:
     Released by [GoReleaser](https://github.com/goreleaser/goreleaser).
 
 gitea_urls:
-  api: https://gitea.com/api/v1
-  download: https://gitea.com
+  api: https://git.lethalbits.com/api/v1
+  download: https://git.lethalbits.com
 force_token: gitea