Remove the mentor immersive rules in shared/shell.css that hid the module
nav, header actions, market tape, overview strip and status bar while
mentorView was active, which made the page look like an independent site.
Mentor now stays inside the canonical 小白复盘 shell and owns its own
"问师 + 数据日期" title header inside #mentorView (B-92 content intact).
Also fix the shell's latent 1024px overflow: .main min-width 1080 now only
applies at >=1280, and the overview strip scrolls internally instead of
clipping its right side when it is wider than the content column.
Update the contract and e2e baselines to assert the shell stays visible
and usable on mentor, page switching leaves no residue, and add a
dedicated shell-integration e2e test.
Co-authored-by: multica-agent <github@multica.ai>
