feat(lsp): add Language Server Protocol server (glint lsp)

New internal/lsp package implements a minimal JSON-RPC 2.0 LSP server
over stdin/stdout with Content-Length framing. Supported lifecycle:
initialize → initialized → shutdown → exit. Document sync: Full (sends
complete text on every change). Handles textDocument/didOpen,
didChange, didSave, didClose; publishes textDocument/publishDiagnostics
after every change. Rule IDs surface as the diagnostic `code` field
with `"glint"` as source. Parse errors produce an Error diagnostic at
the top of the document. Include resolution is best-effort (GITLAB_TOKEN
env var; ~/.cache/glint default cache). CLI: glint lsp [--token]
[--gitlab-url] [--cache-dir] [--offline].

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ROADMAP.md

@@ -97,7 +97,7 @@ The SVG renderer and terminal tree cover the basic layout. These would bring it
 - [x] **GitLab CI template** — shipped v0.2.28; `templates/check.yml` is a GitLab CI/CD Catalog component with `spec:` inputs for stage, file, version, allow_failure, and extra args; also usable as a plain local/remote include
 - [x] **GitHub Actions action** — shipped v0.2.28; `action.yml` composite action downloads the glint Linux binary and runs `glint check`; mirror to GitHub as `k3nny/glint` to reference as `uses: k3nny/glint@v0.2.28`
 - [x] **Pre-commit hook** — shipped v0.2.28; `.pre-commit-hooks.yaml` defines `language: golang` hook; pre-commit builds glint from source on first run and re-runs on staged `.gitlab-ci.yml` changes
-- [ ] **LSP server** — `glint lsp` mode exposing diagnostics over the Language Server Protocol; enables inline squiggles in VS Code, JetBrains, Neovim, etc. without a dedicated extension
+- [x] **LSP server** — shipped v0.2.29; `glint lsp` runs a JSON-RPC 2.0 LSP server over stdin/stdout; `textDocument/didOpen`, `didChange`, `didSave`, `didClose` all publish diagnostics; rule IDs appear as the diagnostic `code`; include resolution is best-effort using env-var token and default cache dir
 - [ ] **VS Code extension** — thin wrapper around the LSP server with syntax highlighting for `.gitlab-ci.yml`
 
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