Improve sessions list rendering on phone layout (#314321)

* Improve sessions list rendering on phone layout

- Phone-aware row height (76px) in SessionsTreeDelegate, refreshed on IsPhoneLayoutContext changes.
- Larger title/details fonts and roomier padding under .phone-layout.
- Card-style row margin/border-radius and centered icon alignment.
- Per-row toolbar always visible on touch; pulled out of the title-row flow with absolute positioning so 44px tap targets do not shift the details row.
- Stop pointer/click propagation at the toolbar container so action taps do not trigger the row open handler.

* Address PR review

- Stop Monaco Gesture tap from reaching the list when the user taps
  an inline action on touch (DOM stopPropagation only covers mouse).
- Drop unsafe vertical margin on the absolutely positioned list row;
  any inter-row spacing lives inside the row via padding/border.
- Refresh stale doc comments (row geometry, iteration cost, no-op
  '2-line wrap' description).