v2.6.2: public endpoint moves to mcp.jmrp.io/gitlab, Fly.io retired

The public HTTP instance is now https://mcp.jmrp.io/gitlab, served alongside
the other MCP servers listed at mcp.jmrp.io. Fly.io is gone from the project:
fly.toml, the fly-debug workflow, the fly-deploy release job and the seven
fly-* Makefile targets are all removed, and this repository now publishes
artifacts only.

BREAKING: the gitlab-mcp-server.fly.dev endpoint no longer exists. Clients
configured against it must move to https://mcp.jmrp.io/gitlab. PRIVATE-TOKEN
is unchanged; GITLAB-URL is now optional and defaults to https://gitlab.com.

Also in this release:
- server.json no longer claims the generic https://{host}:{port}/ remote, which
  was blocking sibling servers from publishing to the MCP Registry
- every check-* freshness gate now runs in CI; check-stats and check-footprint
  had drifted unnoticed and gen_stats no longer derives figures from git history
- every _test.go file is named after the module it tests, which recovered 622
  lines of tests that .gitignore had been excluding from the repository