Initial commit — Antigravity plugin v0.1.0

Plugin Claude Code miroir du plugin codex officiel d'OpenAI, mais
pour Google Antigravity (agy CLI). Headless via:

  agy --print --dangerously-skip-permissions --print-timeout 10m

Includes:
- 1 forwarder agent (antigravity-rescue)
- 5 slash commands (setup, rescue, status, result, cancel)
- 3 internal skills (cli-runtime, result-handling, gemini-prompting)
- agy-companion.mjs runtime (task / setup / status / result / cancel)
- marketplace.json for `/plugin marketplace add`

Tested: setup OK, foreground task OK, background workflow OK
(except OAuth refresh which requires interactive TTY).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

commands/cancel.md

@@ -0,0 +1,15 @@
+---
+description: Cancel a background Antigravity (agy) job
+argument-hint: "<jobId>"
+allowed-tools: Bash(node:*)
+---
+
+Run:
+
+```bash
+node "${CLAUDE_PLUGIN_ROOT}/scripts/agy-companion.mjs" cancel $ARGUMENTS
+```
+
+If no job id is supplied, run `/antigravity:status` first and ask the user which job they want to cancel.
+
+Present the output to the user as-is.