fix(ui): show inline rename text in session sidebar

[fibr]

Summary

• apply the live rename editor layout to the session sidebar as well as the vertical tab rail
• prevent the sidebar tab label's ellipsis paint from hiding the focused input
• add a Chromium regression test covering visible, focused sidebar typing

Verification

• npm run test:browser -- test/inline-rename.test.ts (14 passed)
• npm test (316 files passed, 6,185 tests passed)
• npm run typecheck
• npm run lint
• npm run check:frontend-syntax
• npm run check:public-assets
• npm run format:check
• manually verified the rich sidebar in Chromium: typed text and caret render in the focused editor

[fibr]

Hi, just a small enhancement to the sidebar mode -- i can't see what i'm typing in renaming sessions in the sidebar and this should fix it. Hope it can be taken in :-)

[Ark0N]

Thanks, merged.

Verified rather than taken on trust: with your CSS reverted to master the new test fails with expected 'hidden' to be 'visible', and with it applied the file is 14/14 green (npm run test:browser -- test/inline-rename.test.ts). Good instinct pinning the painted overflow and the input's measured width rather than just the class name, that is the half a class-only assertion would have missed.

One note for whoever touches this next, no action needed here: CLAUDE.md asks rail/sidebar twins to be comma-grouped rather than :is(), because an :is() list takes its most specific argument. It is harmless in this case since both arms are (0,2,1), so the rule lands at (0,5,1) either way, which is what clears the (0,3,1) sidebar clamp further down the file. It would only start to matter if a third arm with a different weight ever joined the list.