feat(chart): layers panel + selection-first fib

- Adds Layers drawer (visible/lock/opacity) and effective opacity wiring.
- Implements selection-first overlay: click selects, drag moves selected, Ctrl-drag edits B, Space-drag always pans.
- Routes pointer events via capture and adds Fib opacity support.
- Updates .gitignore to keep secrets/local scratch out of git.

apps/visualizer/src/features/chart/ChartSideToolbar.tsx

@@ -4,8 +4,8 @@ import {
   IconBrush,
   IconCrosshair,
   IconCursor,
-  IconEye,
   IconFib,
+  IconLayers,
   IconLock,
   IconPlus,
   IconRuler,
@@ -24,7 +24,9 @@ type Props = {
   timeframe: string;
   activeTool: ActiveTool;
   hasFib: boolean;
+  isLayersOpen: boolean;
   onToolChange: (tool: ActiveTool) => void;
+  onToggleLayers: () => void;
   onZoomIn: () => void;
   onZoomOut: () => void;
   onResetView: () => void;
@@ -35,7 +37,9 @@ export default function ChartSideToolbar({
   timeframe,
   activeTool,
   hasFib,
+  isLayersOpen,
   onToolChange,
+  onToggleLayers,
   onZoomIn,
   onZoomOut,
   onResetView,
@@ -195,9 +199,15 @@ export default function ChartSideToolbar({
           </span>
         </button>
 
-        <button type="button" className="chartToolBtn" title="Visibility" aria-label="Visibility" disabled>
+        <button
+          type="button"
+          className={['chartToolBtn', isLayersOpen ? 'chartToolBtn--active' : ''].filter(Boolean).join(' ')}
+          title="Layers"
+          aria-label="Layers"
+          onClick={onToggleLayers}
+        >
           <span className="chartToolBtn__icon" aria-hidden="true">
-            <IconEye />
+            <IconLayers />
           </span>
         </button>
       </div>