Expose machine-readable RC observer handoff

[AetherAI3]

Summary

Expose a single JSON line for aether --json rc start|link|status|off, so a local Predator integration can bind the RC host session and enrolled device to its own browser session without parsing terminal prose. start and link include a fresh short-lived observer invitation; status never replays the one-time link. A failed grant mint leaves the active host session visible with observer: null.

The status projection uses the device ID stored with the active RC session, so a later change in current enrollment does not silently relabel the host. Human output and QR behavior stay as before.

Verification

• TypeScript build passed.
• 47 focused RC host, command, observer handoff, and packaging tests passed.
• Command-level JSON test covers start, status, link, and off in one session and confirms the status line omits the one-time grant.
• Generated documentation and diff whitespace checks passed.
• Production verifier passed: 994 packed files, 4,377,468 bytes, real packed install/launch.
• GitHub required jobs failed before executing steps (empty runner/step lists), and hosted build was neutral. Earlier base revision full suite passed with 2,902 passed and 39 skipped; this PR's changed paths were verified with the focused suite above.

Scope

This is a machine-readable identity handoff prerequisite for AETHER-PREDATOR-M #107. It does not itself publish browser frames through Aether RC or grant model browser control. The RC observer link is a secret until redeemed; callers must not log the start/link JSON line. #107 stays open until the authenticated browser relay and live same-session hand-back are proven.