feat(cli): --version, --help, and strict empty-string validation (e2e-s1.2)

[kumaakh]

Summary

Sprint e2e-s1.2-25826536670 implements 3 P1 issues from .beads/issues.jsonl (label e2e-testing):

• gh-toy-4ef — Add --version / -v flag that prints fleet-e2e-toy v1.0.0 and exits 0 without starting the HTTP server.
• gh-toy-kbk — Add --help / -h flag and help subcommand that print usage info and exit 0 without starting the HTTP server.
• gh-toy-v6z — Reject empty or whitespace-only string arguments for note title and content with a 400 and a clear message. Unit + integration tests added.

CLI handling runs at the very top of src/index.ts so the Express app does not start when only info-flags are requested.

Test plan

• npm run lint — clean
• npm test — 33/33 passing (12 new tests vs main's 21)
• npm run build — clean tsc emit
• node dist/index.js --version → fleet-e2e-toy v1.0.0, exit 0
• node dist/index.js --help → usage listing, exit 0
• POST/PUT /api/notes with empty or whitespace title/content returns 400

Review

Reviewer verdict (committed in feedback.md before cleanup): APPROVED, 0 HIGH findings.