fix(ui): prevent dm avatar shrinking

- Add `flex-shrink: 0` to `.dm-avatar` in `css/tailwind.source.css` to prevent flexbox from resizing avatars inconsistently when space is constrained.
- Rebuild `css/tailwind.generated.css` to apply the changes.
- Verify changes with Playwright script and manual CSS inspection.

css/tailwind.source.css

@@ -5180,6 +5180,7 @@
     display: inline-flex;
     align-items: center;
     justify-content: center;
+    flex-shrink: 0;
     border-radius: var(--radius-full);
     background: var(--surface-sunken);
     color: var(--text-muted);