Improve guided capture session UX

[taggedzi]

What changed

• Consolidates the normal capture workflow into a guided Capture Session page.
• Groups proxy start/stop, portable-browser selection, and launch in the order users need them.
• Adds prominent traffic-inspection and installed-browser profile safety warnings.
• Gates launching behind an explicit dedicated-portable-browser acknowledgement.
• Renames secondary tabs to Capture Rules and Activity, and updates the README.

Why

Previously, users had to move between separate proxy and browser tabs and remember the required order. The browser workflow also did not make mitmproxy credential exposure or installed-profile risks clear enough.

User impact

Users get a simpler three-step setup, safer defaults at the moment of launch, and a clearer place to find advanced settings and activity logs.

Validation

• ./venv/Scripts/pytest.exe -q (80 passed)