v0.4.0

Changelog

• b68cbe9: Add SSH permission audit and one-key chmod fix (@s-johri)
• 95210c5: Add known_hosts browser with confirm-gated entry removal (@s-johri)
• e1eecb5: Add clipboard copy for public key, fingerprint, and ssh command (@s-johri)
• a79729a: Support multiple default identities with legacy migration (@s-johri)
• f2bd214: Detect installed shell-init stub; warn on dup and nudge in TUI (@s-johri)
• c377bcd: Update architecture status to v0.4.0 (@s-johri)