Add Opera / Opera GX to browser cache cleaning

[Vortrix5]

Summary

The browser-cache junk category covers Chrome, Edge, Brave, Vivaldi and Firefox, but not Opera or Opera GX, which are popular and cache a lot.

Where

src/sifty/core/junk.py builds the list of browser User Data roots (see the BraveSoftware / Vivaldi entries around line 44). Opera stores its profile under %APPDATA%\Opera Software\Opera Stable and Opera GX Stable, with the same Cache / Code Cache / GPUCache layout as the other Chromium browsers.

Acceptance criteria

• Opera and Opera GX cache dirs are scanned by sifty junk scan
• Only cache directories, never cookies / history / passwords (match the existing pattern)
• A sandbox test like the existing browser-cache tests
• pytest green

Tip

The /new-junk-category project skill walks through exactly this, including the safety wiring.