Add AWS Device Farm backend and headless simulator commands

[rksm]

Overview

This branch adds AWS Device Farm Test Grid support to the browser simulator and rounds out the CLI/config surfaces needed to run simulator participants without the TUI.

Implements:

• https://linear.app/hyper-video/issue/CORE-2201/investigate-aws-device-farm-as-simulator-backend-and-ios-device
• https://github.com/hypervideo/hyper.video/issues/4961

AWS Device Farm backend

• Adds aws-device-farm as a participant backend kind with device_farm config for project ARN, region, signed URL lifetime, session max duration, idle timeout, and health polling.
• Uses AWS Device Farm desktop browser testing / Test Grid by creating signed Selenium URLs through aws-sdk-devicefarm, then driving remote Chrome over WebDriver with thirtyfour.
• Refactors HyperCore/HyperLite frontend automation behind a driver-agnostic BrowserDriver abstraction so Local Chromium and Device Farm WebDriver share the same join/control/state logic.
• Adds Device Farm session lifecycle handling, WebDriver request URL signing/preservation, state refresh polling, max-duration termination, and best-effort close behavior.
• Adds focused mock-WebDriver integration tests for session creation, signed URL handling, polling/state publication, health-check failure, and session close helpers.
• Documents/handles Device Farm limitations, including synthetic fake media only for remote browsers.

AWS subcommand

• Adds hyper-client-simulator aws list-sessions for the configured Device Farm project, with status filtering, --since, human table output, JSON output, age, and estimated billing totals.
• Supports absolute --since values (YYYY-MM-DD, local date/time, RFC3339) and human-readable relative durations such as --since "1 day".
• Adds hyper-client-simulator aws close-sessions to close explicitly listed session IDs or all active sessions when no IDs are provided.
• Reuses the same device_farm.project_arn, device_farm.region, and signed URL expiration config as the simulator backend.

Headless / no-TUI command

• Adds hyper-client-simulator headless to run participants directly from the CLI without launching the TUI.
• Supports global CLI overrides plus repeated --participant JSON overrides for per-participant URL/backend/media/transport/video/headless settings.
• Adds signal-aware shutdown behavior and headless-specific tests for argument parsing, per-participant overrides, and exit behavior.
• Adds a run-headless-simulator Codex skill for smoke-testing participant runs from the CLI.

Video constraint support

• Replaces the old webcam-resolution enum with Hyper media video constraint values (none, 90p, 144p, 240p, 360p, 480p, 720p, 1080p, 1440p, 2160p).
• Adds publish-webcam and subscribe video constraint settings, plus optional max concurrent video tracks, to config, participant launch specs, participant state, messages, local automation, Cloudflare command/state mapping, remote stub behavior, TUI controls, and the headless CLI.
• Applies video constraints through the frontend hyper.settings.media API for HyperCore; HyperLite keeps unsupported constraint commands as no-ops.

Supporting changes

• Adds AWS/Device Farm/WebDriver dependencies and compile-time Device Farm env wiring for CI/release builds.
• Updates GitHub workflows to provide Device Farm env vars and fetch the private Cloudflare worker submodule with the configured read token.
• Converts the Cloudflare worker schema source to a git submodule and updates README development notes for submodule setup.
• Vendors the patched chromiumoxide_cdp crate needed for the current Chrome CDP event shape used by local browser shutdown/request handling.

Validation

• NIXPKGS_ALLOW_UNFREE=1 nix develop --impure -c just check
  • cargo clippy --all-targets --all-features -- -D warnings
  • cargo nextest run --no-tests warn — 39 root binary tests passed
• NIXPKGS_ALLOW_UNFREE=1 nix develop --impure -c cargo nextest run -p client-simulator-config — 12 passed
• NIXPKGS_ALLOW_UNFREE=1 nix develop --impure -c cargo nextest run -p client-simulator-browser --test device_farm_driver — 5 passed
• git diff --check origin/main...HEAD