fix: resolve agent crash and expand settings sheet

- Move task_dir assignment before VoiceAssistant construction in
  handle_job; UnboundLocalError was crashing every agent job before it
  joined the room, leaving the UI stuck on 'Opening a secure room'
- Make settings sheet full-window height (100dvh) to match tasks panel

web/style.css

@@ -989,17 +989,16 @@ body[data-mode="text"] .mic-meter {
 
 .settings-sheet {
     position: fixed;
+    top: 0;
     left: 50%;
-    bottom: 0;
     z-index: var(--z-sheet);
     width: min(660px, 100%);
-    max-height: min(76vh, 680px);
+    height: 100dvh;
     padding: 0.75rem 1.25rem calc(1.25rem + env(safe-area-inset-bottom));
     display: flex;
     flex-direction: column;
     border: 1px solid var(--line-strong);
-    border-bottom: 0;
-    border-radius: 16px 16px 0 0;
+    border-radius: 16px;
     background: #101e31;
     transform: translate(-50%, 102%);
     transition: transform 240ms var(--ease-out);