T23a round 1 fixes

- your messages shrink within their column and wrap there
- pictures, grids and video take their own shape up to their column's width;
  files, voice notes and link cards stay inside it
- a finished stream shows whole
- avatar pictures load from web addresses too
- the list drops its way down once everything fits again
- the reasoning toggle is a Tab stop with a focus ring
- a link's thumbnail keeps its corners
- gallery: a narrow column of media

TASKS.md

@@ -256,3 +256,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T21c | 2 | PASS | |
 | T22 | 1 | FAIL | a remote cursor scrolled out sideways still drew its flag; presence avatars showed no focus ring; the access list hid roles it could not change; status dots used a fixed size |
 | T22 | 2 | PASS | |
+| T23a | 1 | FAIL | a long message of yours overflowed a narrow column; pictures and video sized to the theme, not their column; a finished stream kept revealing; avatar pictures from the web were read as files; the list stayed away after it fit again; the reasoning toggle had no Tab stop; a link's thumbnail lost its corners |