Add comprehensive settings panel with layout management

New Features:
- Created settings-schema.json with customizable options:
  * Zone appearance (border width, colors, opacity)
  * Show/hide zone numbers
  * Enable/disable Shift+Drag snapping
  * Enable/disable keyboard snapping (Super+Ctrl+1-9)
  * Notification on window snap

- Created settings.js with custom UI:
  * View all saved custom layouts
  * Delete custom layouts with confirmation dialog
  * Export layouts to JSON files
  * Visual list with layout info (name, zone count, ID)
  * Empty state when no custom layouts exist

Extension Integration:
- Integrated Settings API into extension.js
- Zone overlay now respects user-configured colors and opacity
- Border width is customizable
- Zone numbers can be toggled on/off
- Shift-drag and keyboard snap can be disabled via settings
- Optional notifications when windows snap to zones
- Settings properly cleaned up on extension destroy

UI/UX Improvements:
- Professional settings panel accessible from System Settings → Extensions
- Layout management without editing JSON files manually
- Real-time application of visual settings
- Destructive actions (delete) require confirmation
- Export functionality for sharing layouts

Fixes TODO item #12 - Settings Panel
Fixes TODO item #13 - Update Metadata (already done)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

settings-schema.json

@@ -0,0 +1,57 @@
+{
+    "show-zone-numbers": {
+        "type": "checkbox",
+        "default": true,
+        "description": "Show zone numbers in overlay",
+        "tooltip": "Display zone numbers when the overlay is visible"
+    },
+    "zone-border-width": {
+        "type": "spinbutton",
+        "default": 2,
+        "min": 1,
+        "max": 10,
+        "step": 1,
+        "units": "pixels",
+        "description": "Zone border width",
+        "tooltip": "Width of the zone border in the overlay"
+    },
+    "zone-opacity": {
+        "type": "scale",
+        "default": 20,
+        "min": 0,
+        "max": 100,
+        "step": 5,
+        "description": "Zone overlay opacity",
+        "tooltip": "Opacity of zone fill color (percentage)"
+    },
+    "enable-shift-drag": {
+        "type": "checkbox",
+        "default": true,
+        "description": "Enable Shift+Drag snapping",
+        "tooltip": "Show zones and snap windows when dragging with Shift held"
+    },
+    "enable-keyboard-snap": {
+        "type": "checkbox",
+        "default": true,
+        "description": "Enable keyboard snapping (Super+Ctrl+1-9)",
+        "tooltip": "Allow snapping windows to zones using keyboard shortcuts"
+    },
+    "notification-on-snap": {
+        "type": "checkbox",
+        "default": false,
+        "description": "Show notification when window snaps",
+        "tooltip": "Display a notification when a window is snapped to a zone"
+    },
+    "zone-border-color": {
+        "type": "colorchooser",
+        "default": "rgba(100, 149, 237, 0.8)",
+        "description": "Zone border color",
+        "tooltip": "Color of the zone borders"
+    },
+    "zone-fill-color": {
+        "type": "colorchooser",
+        "default": "rgba(100, 149, 237, 0.2)",
+        "description": "Zone fill color",
+        "tooltip": "Color of the zone fill"
+    }
+}