feat(launch): show session id prefix in resume picker

[rsridhr]

What

The launch --resume picker lists a project's sessions by first message + timestamp (+ account path when multiple accounts exist), but never shows the session id. Since --session <id> needs that id and each row otherwise looks similar, there was no way to tell which session a row maps to.

This prepends the 8-char session-id prefix to each row label:

a7f36f7f  Refactor the auth middleware       Jul 17 10:18pm  ~/.claude2
1b2c3d4e  Investigate flaky CI test          Jul 17 10:18pm  ~/.claude
5f6a7b8c  Draft release notes for v2         Jul 17 10:17pm  ~/.claude2

Details

• Scoped to the interactive picker only (the default: branch in runLaunch). The --session <id>, --resume, and single-session fast paths are untouched.
• Selection still resumes by the full internal sess.sessionID; the prefix is display-only.
• Added a small shortSessionID helper (safe byte-slice — session ids are ASCII UUIDs).

Testing

• gofmt / go vet / go build ./... clean, go test ./... passes.
• Verified manually with multiple sessions across two accounts (~/.claude, ~/.claude2) — the id prefix renders correctly and selection resumes the right session.

🤖 Generated with Claude Code