#95 Honest install-only UX and Nu-agnostic try fallbacks

Summary

• search / info: scripts and completions report install-only (activation deferred) instead of module-style ABI labels
• numan try: prefer activatable curated starters; fall back to SuaveIV/nu_script_wttr then Sanceilaks/nufetch; skip activate for install-only types and print overlay use guidance
• Pin offer still only applies to activatable curated starters

Test plan

• cargo test --lib select_starter / install-only search+info tests
• cargo clippy -- -D warnings
• After registry Wave 3B is on CDN: numan search cargo etc.; numan try with no plugin starter installs a script without activation error