Cookie Manager

> ℹ️ _This issue was partially AI-generated and may contain technical inaccuracies._

**Is your feature request related to a problem? Please describe.**
Cookie handling is only possible by manually setting `Cookie` headers; there is no visibility into cookies received from responses or persistence across requests/sessions.

**Describe the solution you'd like**
Add a dedicated Cookie Manager UI to view, add, edit, and delete cookies, with a cookie jar that persists cookies across requests and sessions (per domain).

**Describe alternatives you've considered**
Manually copying `Set-Cookie` values into `Cookie` headers on each request (current workaround).

**Additional context**
Should respect domain/path/expiry attributes and integrate with session/auth flows.

No files, tests, or entry points are named. Start by locating the existing Cookie header handling and session/auth flows, then determine how UI state and per-domain persistence are organized. Done means users can view, add, edit, and delete cookies, with domain, path, and expiry behavior preserved across requests and sessions.

Written by the indexing model from the issue text.