Choose a linked computer for transcription #1890

Feature / improvement for Solenta. Priority: Medium. Area: Speech.

Explicit per-device opt-in to a named authenticated host, with cancellation on revocation and no automatic destination switch. Useful for clients without a local runtime. Depends on an intentional product decision to transmit audio.

Acceptance criteria:

• Implement the described behavior through existing shared APIs and UI; preserve explicit settings and account/permission boundaries.
• Cover the stated edge cases with focused regression checks and run the relevant typechecks/tests.
• Verify affected visible UI behavior and document platform/dependency limits.

Part of #1869.