Fix client-side-redirect

[mjudeikis]

After #351 was merged, redirect handling was left not in the ideal state.

Look for the issue link in the code for more details.

We should update web application to store cli sessionID and redirect URL and construct its own url. Backend should not need to know about client side redirects.

[coderabbitai]

A summary of the changes CodeRabbit can apply:

• Fix handler.go by removing the incorrect line 510 and inserting an explanatory TODO comment at line 27, and update backend/template/resources.gohtml to inject client-side redirect JS (including reading callback port from URL and calling /bind via fetch), add CallbackPort to the UI data passed to the template, and replace the bind anchor with a JavaScript-driven button that performs the redirect.

• Update backend/http/handler.go to stop storing a full redirect URL and instead store/validate a callback port (rename messages accordingly), set cookie secure=false for localhost, append the callback port as a query param when redirecting to resources, replace server‑side redirects in the bind flow with a JSON response containing the base64-encoded response for client‑side redirect, and remove unused server‑side helper output (HTML write and related helper functions).

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