Add optional task-scoped Android testing for coding agents

[witbrock]

Adds optional task-scoped Android testing to coding-agent instances, reusing the operator registry and capacity lock. The existing coding controller handles native requests without passing credentials to its coding child; screenshots and reports return through canonical task attachments.

Ready to merge after core PR682, now merged. Current-main integration preserves timing, token accounting, retry and supervision. 131 focused tests pass. Prior native emulator/controller acceptance remains valid: its unchanged host/controller/service files have not been altered during integration, so no emulator campaign was repeated.

• Private disposable AVDs, explicit RAM/CPU budgets, native taps/text, named fixtures, screenshots and environment reports.
• Current assignment/delegator/organisation checks, private SSH socket transport, deduplicated intents and symlink-safe request mailboxes.
• The retained live controller-to-Mac acceptance verified Android17, Chrome145, Gboard17.2, 3GiB RAM/two cores, native text/tap, replay, duplicate launch, capacity refusal and other-organisation denial. Three canonical attachment byte hashes matched.
• Interrupting the supervisor stopped emulator/ADB, removed disposable data/socket and released capacity; terminal replay did not restart it. Temporary relay removed.

Same-host nested coding/emulator reservations remain unsupported by the single-slot baseline; the intended DGX/Mac route has separate host budgets. Chrome152 and physical devices are outside acceptance. Publishing does not activate a production Android registry, host relay or default emulator launch.

Task: #V#task_add_optional_androidemulator_testing_to_53400265. Evidence: docs/engineering/coding_agent_android_testing.md and canonical task attachments. Parent VS Code owner handles native close-out and the separately authorised final deployment.

[witbrock]

Quick integration review against main a607464: this branch contains the unmerged PR682 base and has worker merge conflicts. Integrate against the accepted final PR682 rather than merging both old worker snapshots independently. The shared host-capacity lock serialises coding and emulator launches; same-host nested coding/emulator work is not supported by this baseline. Preserve the validated DGX-to-Mac separate-host route and verify cleanup/interruption with the integrated worker. No fresh end-to-end test was run for this quick review.