feat: add TUI session orchestrator

Add a first-class active-session orchestrator for the Ink TUI:

- list, activate, close, and launch live process-local TUI sessions
- hydrate committed and in-flight output when switching sessions
- dispatch a new prompt session from the +new row with session-scoped model picks
- expose a clickable live-session count in the status chrome
- preserve stable row order while initially focusing the current session
- support mouse hit-testing for floating orchestrator overlays
- add backend and frontend regression coverage for the lifecycle and UI helpers

ui-tui/src/components/appLayout.tsx

@@ -252,7 +252,11 @@ const ComposerPane = memo(function ComposerPane({
           cols={composer.cols}
           compIdx={composer.compIdx}
           completions={composer.completions}
+          onActiveSessionSelect={actions.activateLiveSession}
+          onActiveSessionClose={actions.closeLiveSession}
           onModelSelect={actions.onModelSelect}
+          onNewLiveSession={actions.newLiveSession}
+          onNewPromptSession={actions.newPromptSession}
           onPickerSelect={actions.resumeById}
           pagerPageSize={composer.pagerPageSize}
         />
@@ -354,9 +358,11 @@ const StatusRulePane = memo(function StatusRulePane({
         busy={ui.busy}
         cols={composer.cols}
         cwdLabel={status.cwdLabel}
+        liveSessionCount={ui.liveSessionCount}
         model={ui.info?.model ?? ''}
         modelFast={ui.info?.fast || ui.info?.service_tier === 'priority'}
         modelReasoningEffort={ui.info?.reasoning_effort}
+        onSessionCountClick={() => patchOverlayState({ sessions: true })}
         sessionStartedAt={status.sessionStartedAt}
         showCost={ui.showCost}
         status={ui.status}