Uninstall self-hosted machines

[SaladDay]

What

• New oac-daemon uninstall (run as the installation's bin/oac-daemon): stops the daemon, lists what it deletes (installation directory with credential file, native history and Harnesses; the native-download directory with the download lock), asks [y/N], deletes, and prints the Web follow-up (Revoke in Executor credentials, or Delete the Session). The workspace is never deleted, and uninstall refuses if it sits inside the installation directory. A second run in an empty place prints that nothing is installed and exits 0. On Windows the running exe is kept, everything else is deleted, and a detached cmd removes the rest after exit.
• The daemon started by oac-daemon start now exits with the rejection message (credential revoked/rotated, Session deleted, binding conflict, incompatible version) instead of parking, so a later start reports the same reason. This is selected by an explicit exitOnRejection argument of runEnvironmentConnect; oac-daemon connect (Docker unless-stopped) still parks. The native message names oac-daemon start / oac-daemon uninstall.
• Docs: new "Remove a machine" section, reboot note, uninstall row, rejected-daemon behaviour (EN + zh, source_hash refreshed); credential contract line updated (EN + zh).
• Smoke: native-onboarding-smoke.mjs ends with an uninstall step.

Why

Audit F5 (no removal command or docs, daemon parks forever, no reboot note); decisions 1 and 4.

Justification of new surface

• uninstall command: the user decision. No flag: no unattended caller exists, so confirmation is always interactive.
• exitOnRejection parameter: explicit selection from the native start path; no name check.

Verification

• go test ./apps/daemon/internal/cli pass; go vet ./... pass; GOOS=windows go vet ./apps/daemon/... pass.
• python3 scripts/check-names.py pass; translation guard tests 1-2 pass.
• Skipped: translation test 3 (needs vitepress); local native-onboarding-smoke.mjs (needs the full CI bundle build), left to the Native workflow.

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