changelog: Gemini CLI host and contributor marker (#1247, #3447)

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

changelog.d/gsta222-gemini-host-contributor-marker.md

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+**gstack installs into Gemini CLI, and installs made before v1.91.231.0 finally drop the test and eval packages they never needed.** `./setup --host gemini` puts every gstack skill in `~/.gemini/skills`, where Gemini CLI 0.66.0 lists them (#1247). Separately, `./setup` used to treat any checkout that had TypeScript installed as a contributor's, so every install made before v1.91.231.0 (which ran a full `bun install`) kept about 510 MB of dev packages in `node_modules` forever (#3447).
+
+### Added
+- **Gemini CLI host** (experimental): `./setup --host gemini` (alias `gemini-cli`; `--host auto` picks it only when `gemini` is on PATH) links `gstack-<skill>` directories into `~/.gemini/skills` plus the `~/.gemini/skills/gstack` runtime root. The render goes to `.gemini-cli/` with frontmatter names that match their directories, `CLAUDE.md` read as `GEMINI.md`, and a tool glossary for Gemini CLI's tool names and for Antigravity CLI, which can read the same folder. Ask for a skill by name (`gstack-office-hours`); Gemini CLI loads it with `activate_skill`. `gstack-uninstall` removes only gstack-managed entries there, so your own skills stay. `--local --host gemini` is refused with a note that Gemini CLI loads workspace skills only in trusted folders. docs/ADDING_A_HOST.md lists the verified facts.
+- **An explicit contributor marker**: `bin/dev-setup` runs `git config gstack.contributor true`, and `GSTACK_CONTRIBUTOR=1` marks a single run. A marked clone keeps the full install on every `./setup`.
+
+### Changed
+- **An unmarked clone that still has the dev toolchain moves to production dependencies once.** setup takes a lock in the checkout, moves `node_modules` aside, installs production dependencies, checks every runtime package resolves, then deletes the old copy. If the install fails, the full `node_modules` goes back and setup prints `SETUP_DEPS_MIGRATE_FAILED` with the cause; nothing is removed and the next `./setup` tries again. CI, and a checkout whose git config cannot be read, never migrate. On a real install `node_modules` went from 1079 MB to 569 MB. Bun's shared package cache is left alone, because other projects can read it through symlinks.
+
+### Tests
+- test/setup-production-deps.test.ts: the marker (git config, env, CI, unreadable git config), the one-time migration and its no-op rerun, restore on a failed or unverified install, recovery of an interrupted move, the lock, an untouched Bun cache, and a real-Bun fixture for a marked and an unmarked clone. test/uninstall.test.ts: Gemini CLI entries removed, the user's own kept. Host config, conformance, install-registry, render-prune and runtime-root tests cover the new host.