Refine conversation visual affordances

[thomaspblock]

Summary

• Refine conversation timeline visuals: lighter beginning divider, text-only reply-summary hover, and last-reply timing.
• Add hoverable profile popovers for inline mentions and system-message names, including dual avatars for add/remove member events.
• Stabilize the desktop channel-browser shortcut smoke test on macOS.

Test plan

• just ci
• cd desktop && pnpm check
• cd desktop && pnpm exec playwright test --project=smoke tests/e2e/channel-browser.spec.ts:19
• cd desktop && pnpm exec playwright test --project=smoke tests/e2e/channel-browser.spec.ts:19 tests/e2e/channels.spec.ts:405
• cd desktop && pnpm exec playwright test --project=smoke

Made with Cursor

[thomaspblock]

visualfixes.mp4