Carry a copyright line and an SPDX license identifier in every source file #1546

No source file carries a copyright line or a license identifier: none of the roughly 3,185 tracked .go files and none of the roughly 141 shell, Python, JavaScript, TypeScript, Astro, CSS, PowerShell and Ruby files. LICENSE says "Copyright (c) 2026 Jose Manuel Requena Plens". The OpenSSF Best Practices gold criteria copyright_per_file and license_per_file ask for both in every source file, and suggest "Copyright the [project name] contributors." with an SPDX identifier.

Change

• The holder is the maintainer's decision: "Copyright the gitlab-mcp-server contributors." (with LICENSE naming the contributors too) or the maintainer's name.
• Two comment lines near the top of every source file, the copyright line and SPDX-License-Identifier: MIT: every .go file, testdata included, and .sh, .py, .mjs, .js, .ts, .astro, .css, .ps1, .rb, Dockerfile and Makefile. Data and prose (JSON, YAML data, Markdown, MDX) are not source.
• Placement: separated from the package clause by a blank line so go/doc does not read it as the package comment (go run ./cmd/godoc_tool/ audit stays clean); after the shebang in scripts; inside the frontmatter in .astro; Code generated ... DO NOT EDIT. kept intact.
• The generators that write source emit the header (cmd/gen_action_catalog_manifest, cmd/gen_action_grants, cmd/gen_brand and any other), and the templates that create files (the create-mcp-tool skill) carry it.
• A gate in Go over internal/sourcewalk, with a fix mode, run by make analyze and CI; CLAUDE.md gets the rule and a link.
• Tests that assert file:line positions in testdata are updated for the shifted lines.

The change touches every source file, so it is produced by the gate's fix mode and regenerated on the current main right before it merges, when no other stack is open, rather than rebased.

Done when

• The gate passes on the tree and fails on a planted file without the header.
• go build ./..., go test ./..., golangci-lint, the Go doc audit, every generator's -check and the site gates pass.