fix(gmail): correct draft send tip - #915

Description

Fixes #914.

The tip printed after creating a Gmail draft now uses the CLI's space-separated Discovery subcommands, passes userId through --params, and sends the draft ID in the request body with --json. The command is kept in a tested constant so the user-facing example stays covered.

Dry Run Output:

{
  "body": {
    "id": "draft-test"
  },
  "dry_run": true,
  "is_multipart_upload": false,
  "method": "POST",
  "query_params": [],
  "url": "https://gmail.googleapis.com/gmail/v1/users/me/drafts/send"
}

Checklist:

• My code follows the AGENTS.md guidelines (no generated google-* crates).
• I have run cargo fmt --all to format the code perfectly.
• I have run cargo clippy -- -D warnings and resolved all warnings. The command is currently blocked by pre-existing warnings on origin/main under Rust 1.97 (first at helpers/script.rs:173); the stricter all-target run reproduces the same baseline findings on an unmodified worktree.
• I have added tests that prove my fix is effective or that my feature works.
• I have provided a Changeset file to document my changes.

Validation: focused regression test passed; the full workspace test suite passed (82 library tests and 702 CLI tests); git diff --check passed.