feat(extension): allow configuring Browser Bridge daemon port

[Mr0bean]

Summary

Adds daemon port configuration support to the Browser Bridge extension so it can match OPENCLI_DAEMON_PORT in multi-profile or managed-browser environments.

Priority order:

1. Saved extension setting from chrome.storage.local (opencli_daemon_port_v1), editable from the extension popup.
2. Build-time OPENCLI_DAEMON_PORT injected by the extension Vite build.
3. Default fallback port 19825.

Why

The CLI and daemon already support OPENCLI_DAEMON_PORT, but the extension previously used a build-time constant. That made it difficult for managed environments to run multiple isolated Browser Bridge daemon ports without rewriting the built extension output.

Changes

• Replaces fixed extension daemon URLs with runtime URL builders.
• Adds port parsing and fallback helpers.
• Adds popup UI for manually saving/resetting the daemon port.
• Injects OPENCLI_DAEMON_PORT during extension builds via Vite.
• Documents custom daemon port usage.
• Adds extension tests for port resolution priority and validation.

Verification

• npm run typecheck --prefix extension
• npx vitest run --project extension extension/src/background.test.ts
• npx vitest run --project extension
• OPENCLI_DAEMON_PORT=23456 npm run build --prefix extension verified build-time injection
• npm run build --prefix extension rebuilt committed dist with default fallback