feat(cli): persist startup defaults from XDG config

[joebasrawi]

Summary

The standalone chrome-devtools CLI auto-starts its daemon when the first tool command runs, but that path had no way to reuse user-specific startup options (executablePath, headless, userDataDir, and other start flags). After a reboot, crash, or stop, the next command launched the daemon with built-in defaults.

This adds an XDG-compatible config file:

$XDG_CONFIG_HOME/chrome-devtools/config.json

falling back to ~/.config/chrome-devtools/config.json. For example:

{
  "executablePath": "/usr/bin/chromium",
  "headless": false
}

Precedence is:

explicit command-line options > configuration file > built-in defaults

The same file is applied to automatic daemon startup and to explicit chrome-devtools start when an option is omitted. Config keys are validated with the existing start option parser (including coerce/conflict rules). chrome-devtools status continues to report the effective daemon arguments.

Fixes #2388

Design notes

Implemented against current main rather than resurrecting closed PR #2389.

• Config loading lives in src/config/cli-config.ts next to the current option modules.
• Auto-start and start share getCliStartOptions(), applyCliStartDefaults(), and yargs .config(), so CLI-specific defaults such as isolated stay consistent.
• Auto-start no longer serializes the tool command’s argv into daemon flags. Tool commands do not register start options, and overlapping keys (for example viewport on emulate) could leak into the daemon. Persistent defaults belong in the config file; explicit chrome-devtools start --… still overrides them.
• Unknown or invalid config keys fail with the same validation as chrome-devtools start.

Testing

• Unit tests for config path resolution, missing/invalid files, option validation, and CLI > config > built-in precedence (tests/cli-config.test.ts)
• E2E: automatic list_pages startup uses config values and status shows them
• E2E: explicit start uses config when flags are omitted
• E2E: command-line flags override config

Locally: npm run format, npx tsc --noEmit, npm run test tests/cli-config.test.ts, and the chrome-devtools start/commands e2e files.

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