GIMP-like UI overhaul - toolbar, sidebar, full-width canvas

- Redesign layout: left toolbar, center canvas, right sidebar
- Add vertical tool strip with keyboard shortcuts (V, R, E, F, W, B, G, Z, H)
- Collapsible sidebar panels: Tool Options, AI Edit, Quick Actions, Eyes, Layers, History
- Canvas now fills available space with checkerboard background
- Add zoom controls in status bar
- Add menu bar with New, Save, Reset
- Remove old multi-column layout

frontend/src/components/ImageCanvas.css

@@ -1,45 +1,48 @@
+/* ImageCanvas fills the entire canvas wrapper */
 .canvas-container {
-  position: relative;
-  width: 100%;
-  height: 100%;
-  min-height: calc(100vh - 180px);
-  background-color: #2a2a2a;
-  border: 2px solid #444;
-  border-radius: 8px;
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
   overflow: hidden;
-  display: flex;
-  align-items: center;
-  justify-content: center;
 }
 
 .canvas-container canvas {
   display: block;
 }
 
+/* Selection hint */
+.selection-hint {
+  position: absolute;
+  bottom: 40px;
+  left: 50%;
+  transform: translateX(-50%);
+  background-color: rgba(0, 0, 0, 0.8);
+  color: #0088ff;
+  padding: 6px 12px;
+  border-radius: 4px;
+  font-size: 11px;
+  z-index: 10;
+  white-space: nowrap;
+  pointer-events: none;
+}
+
+/* Clear selection button */
 .clear-selection-btn {
   position: absolute;
-  top: 10px;
-  right: 10px;
-  background-color: #ff4444;
+  top: 8px;
+  right: 8px;
+  background-color: #cc3333;
   color: white;
-  padding: 8px 16px;
+  padding: 6px 12px;
+  font-size: 11px;
+  border: none;
+  border-radius: 3px;
+  cursor: pointer;
   z-index: 10;
 }
 
 .clear-selection-btn:hover {
-  background-color: #cc0000;
-}
-
-.selection-hint {
-  position: absolute;
-  bottom: 10px;
-  left: 50%;
-  transform: translateX(-50%);
-  background-color: rgba(0, 0, 0, 0.8);
-  color: #00ff00;
-  padding: 8px 16px;
-  border-radius: 4px;
-  font-size: 12px;
-  z-index: 10;
-  white-space: nowrap;
+  background-color: #dd4444;
 }