refactor(workspace): match KnowledgeView mini-chat dock style

- Widget is now a bottom-anchored dock spanning the content width
  (max-width 1200px, rounded top corners, bg-secondary, upward shadow)
  instead of a floating corner box.
- Drop the closed state and ✕ button — widget is always present,
  matching KnowledgeView's pattern. Collapsed = input-only dock,
  expanded = full ChatPanel above the input.
- Grid ratio 1fr:2fr → 0.85fr:2.15fr so tasks get a touch less room
  and notes a touch more.
- Workspace note-rail (the notes picker column inside the editor)
  widens from 155px to 200px so note titles breathe.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/WorkspaceView.vue

@@ -45,8 +45,8 @@ const panelOpen = ref<{ tasks: boolean; notes: boolean }>({ tasks: true, notes:
 
 const gridColumns = computed(() => {
   return [
-    panelOpen.value.tasks ? "minmax(0, 1fr)" : "0px",
-    panelOpen.value.notes ? "minmax(0, 2fr)" : "0px",
+    panelOpen.value.tasks ? "minmax(0, 0.85fr)" : "0px",
+    panelOpen.value.notes ? "minmax(0, 2.15fr)" : "0px",
   ].join(" ");
 });