[iuyo5678]

Support optional local authentication before browser registration and business traffic. Paired peers prove their local keys, while Warn-mode daemons accept existing extension handshakes. Required mode remains an explicit policy choice.

The protocol validates proofs, identity binding, rotation and saved-candidate recovery before granting authenticated access. The later paired-identity protection PR prevents legacy peers from impersonating an activated browser while keeping unrelated unpaired browsers usable.

Validation across the final stack:

• Rust workspace: 1,020 passed, one existing ignored; formatting and strict Clippy.
• Extension: 3,570 passed, 363 environment-dependent skips; TypeScript, Biome and production build.
• Five real-daemon tests using the current CLI and published 0.4.1; real Chrome for Testing pairing/navigation smoke.
• The 0.4.2 stage independently passed 131 focused tests, three real-daemon tests, typecheck and Biome.

Stack 3/9; base: #425. Review order: #424 → #425 → #426 → #427 → #428 → #429 → #430 → #431 → #432.