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/sse-events.ts

@@ -5,7 +5,7 @@
  * and referenced by the frontend (`SSE_EVENTS` in `constants.js`).
  * Both files MUST be kept in sync.
  *
- * 157 event constants organized by category:
+ * 158 event constants organized by category:
  * - **Core** (1): init
  * - **Transport** (1): sse:heartbeat
  * - **Session lifecycle** (23): created, updated, deleted, terminal, idle, working, ...
@@ -25,7 +25,7 @@
  * - **Plan orchestration** (5): started, progress, subagent, completed, cancelled
  * - **Tunnel** (7): started, stopped, progress, error, qrRotated, qrRegenerated, qrAuthUsed
  * - **Image / attachments** (2): image:detected, attachment:detected
- * - **Hooks** (9): idle_prompt, permission_prompt, elicitation_dialog, elicitation_complete, elicitation_response, stop, agent_working, teammate_idle, task_completed
+ * - **Hooks** (10): idle_prompt, permission_prompt, elicitation_dialog, elicitation_complete, elicitation_response, stop, agent_working, teammate_idle, task_completed, prompt_submitted
  *   (agent_working is the odd one out: reported by the DeepSeek Harness status bridge, not by a Claude Code hook)
  * - **Approvals** (3): pending, updated, resolved (cross-session Approvals Inbox)
  * - **Orchestrator** (12): stateChanged, planProgress, planReady, phase*, verification, task*, completed, error
@@ -372,6 +372,8 @@ export const HookAgentWorking = 'hook:agent_working' as const;
 export const HookTeammateIdle = 'hook:teammate_idle' as const;
 /** Claude Code hook: teammate task completed. */
 export const HookTaskCompleted = 'hook:task_completed' as const;
+/** UserPromptSubmit fired in a Claude pane (#367): the pane learned its live conversation id first-hand. */
+export const HookPromptSubmitted = 'hook:prompt_submitted' as const;
 
 // ─── Approvals Inbox ─────────────────────────────────────────────────────────