feat: integrate Coloris color picker for background field

Add Coloris.js library for enhanced color selection in PageSettings with
automatic button state sync across tab changes.

Features:
- Color picker with swatches, alpha support, and format toggle (hex/rgb/hsl)
- Button positioned to the left of input field
- Automatic sync when switching tabs (remembers selected color)
- Close button and click-outside-to-close functionality
- Dark theme with pill UI style

Changes:
- Install @melloware/coloris package
- PageSettings.vue: Integrate Coloris with data-coloris attribute,
  add tab visibility detection via provide/inject, force button update
  when returning to document tab
- EditorPanel.vue: Provide activeTab to child components, increase
  panel width to 30rem
- _forms.scss: Add .input-with-color styles with custom Coloris
  button positioning (absolute positioned to left of input)
- Temporarily comment out rgb/hex format buttons (replaced by Coloris
  format toggle)

Technical details:
- Uses provide/inject pattern to detect tab changes
- Triggers synthetic input events to force Coloris button refresh
- Custom CSS overrides to position swatch button correctly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

package-lock.json

@@ -8,6 +8,7 @@
       "name": "geoproject",
       "version": "0.0.0",
       "dependencies": {
+        "@melloware/coloris": "^0.25.0",
         "highlight.js": "^11.11.1",
         "pagedjs": "^0.4.3",
         "pinia": "^3.0.4",
@@ -532,6 +533,12 @@
       "integrity": "sha512-cYQ9310grqxueWbl+WuIUIaiUaDcj7WOq5fVhEljNVgRfOUhY9fy2zTvfoqWsnebh8Sl70VScFbICvJnLKB0Og==",
       "license": "MIT"
     },
+    "node_modules/@melloware/coloris": {
+      "version": "0.25.0",
+      "resolved": "https://registry.npmjs.org/@melloware/coloris/-/coloris-0.25.0.tgz",
+      "integrity": "sha512-RBWVFLjWbup7GRkOXb9g3+ZtR9AevFtJinrRz2cYPLjZ3TCkNRGMWuNbmQWbZ5cF3VU7aQDZwUsYgIY/bGrh2g==",
+      "license": "MIT"
+    },
     "node_modules/@rolldown/pluginutils": {
       "version": "1.0.0-beta.50",
       "resolved": "https://registry.npmjs.org/@rolldown/pluginutils/-/pluginutils-1.0.0-beta.50.tgz",