fix(hooks,mobile): the merge-time items from the #367 and #368 reviews

#367 (UserPromptSubmit hook): `hook:prompt_submitted` went on the wire
unregistered; it is now in both SSE registries (158 = 158), and the hook only
lands in the run summary when the conversation actually moved, since one row
per prompt would evict useful rows from the 1000-event FIFO and clutter the
Summary timeline and /api/search.

#368 (Add Case header submit): the pending-state dimming targeted the footer
button, which the <=860px layout hides, so on a phone the only visible submit
control stayed at full brightness while a clone ran. The header button now
dims too, and a static test pins the header-submit contract so it cannot
silently disappear again.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/web/public/constants.js

@@ -958,6 +958,7 @@ const SSE_EVENTS = {
   HOOK_AGENT_WORKING: 'hook:agent_working',
   HOOK_TEAMMATE_IDLE: 'hook:teammate_idle',
   HOOK_TASK_COMPLETED: 'hook:task_completed',
+  HOOK_PROMPT_SUBMITTED: 'hook:prompt_submitted',
 
   // Approvals Inbox
   APPROVAL_PENDING: 'approval:pending',