enable exit node selector

[e-kotov]

Would close #5

[Copilot]

Pull request overview

Adds exit node selection support to the browser extension by exposing exit node list/set commands from the native Go host and wiring a dropdown selector into the Chrome/Firefox popups.

Changes:

• Add native-host commands to fetch available exit nodes and set/clear the selected exit node.
• Add popup UI (HTML/CSS/JS) to display and change the exit node selection.
• Extend background scripts to forward popup requests to the native host and return responses.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
ts-browser-ext.go	Implements get-exit-nodes and set-exit-node commands and adds request/reply JSON fields for exit node control.
background.js	Adds Chrome background message plumbing for exit node get/set operations.
popup.js	Adds Chrome popup dropdown UI logic to fetch, display, and change exit node selection.
popup.html	Adds Chrome popup dropdown markup/styles for exit node selection.
firefox/background.js	Adds Firefox background message plumbing for exit node get/set operations; also adjusts proxy handler management.
firefox/popup.js	Adds Firefox popup dropdown UI logic to fetch, display, and change exit node selection.
firefox/popup.html	Adds Firefox popup dropdown markup/styles for exit node selection.

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