fix(gui): keep the parallel-active count outside the ellipsized hint

Both todo one-line surfaces truncate the active hint with overflow: hidden
and text-overflow: ellipsis. A "+N" appended to the first active task's name
therefore sat at the far end of the truncatable text, so a long task name or a
narrow viewport clipped exactly the part that reports the other running tasks,
leaving a parallel plan indistinguishable from a sequential one.

planSummary now returns activeContent and activeExtra as separate fields
instead of one joined activeHint, and each surface renders the count in its own
flex: none span beside the ellipsized name: .activeExtra in the collapsed plan
strip header, .extra in the todo_write row. Putting the count in front of the
name was rejected — the task name is what the reader looks for first.

The parallel-plan cases in todo-panel.spec.tsx now assert the count is a
separate element from the name, and both fail if the two are rejoined. The
assembled web snapshot re-records: the flex gap supplies the visual space, so
the transcript reads "实现 fixture 样本+1" with no space in the text nodes.

packages/client/ui-conversation/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/client/ui-conversation/README.md
-README.md: 5b12242ac3f477233bd7e897261a9a0c2478aa41
-README.zh.md: 6076e706b2e6e80775149ebcf7c55ab478b41f18
+README.md: 4df6712d3beb980f564650ca39caa1e77d8fdb4e
+README.zh.md: 7ff3d36867296ee1d870e189bc5103e8cea12731