fix: correct API integration and complete missing features

Fix API response format mismatches and implement all remaining features:

**API Integration Fixes:**
- Fix ManipulationPanel to use `colors` instead of `results` from API responses
- Fix gradient endpoint to use `gradient` array from API response
- Fix color blindness simulator to use correct field names (`input`/`output` vs `original`/`simulated`)
- Fix text color optimizer request field (`backgrounds` vs `background_colors`)
- Fix method name casing: `simulateColorBlindness` (capital B)
- Add palette generation endpoint integration

**Type Definition Updates:**
- Update GradientData to match API structure with `gradient` array
- Update ColorBlindnessData to use `colors` with `input`/`output`/`difference_percentage`
- Update TextColorData to use `colors` with `textcolor`/`wcag_aa`/`wcag_aaa` fields
- Add PaletteGenerateRequest and PaletteGenerateData types

**Completed Features:**
- Harmony Palettes: Now uses dedicated `/palettes/generate` API endpoint
  - Simplified from 80 lines of manual color theory to single API call
  - Supports 6 harmony types: monochromatic, analogous, complementary, split-complementary, triadic, tetradic
- Text Color Optimizer: Full implementation with WCAG compliance checking
  - Automatic black/white text color selection
  - Live preview with contrast ratios
  - AA/AAA compliance indicators
- Color Blindness Simulator: Fixed and working
  - Shows difference percentage for each simulation
  - Side-by-side comparison view
- Gradient Creator: Fixed to use correct API response structure
- Batch Operations: Fixed to extract output colors correctly

**UI Improvements:**
- Enable all accessibility tool cards (remove "Coming Soon" badges)
- Enable harmony palettes card
- Add safety check for gradient state to prevent undefined errors

All features now fully functional and properly integrated with Pastel API.

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

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

app/palettes/gradient/page.tsx

@@ -28,8 +28,8 @@ export default function GradientPage() {
         count,
         colorspace,
       });
-      setGradient(result.colors);
-      toast.success(`Generated ${result.colors.length} colors`);
+      setGradient(result.gradient);
+      toast.success(`Generated ${result.gradient.length} colors`);
     } catch (error) {
       toast.error('Failed to generate gradient');
     }
@@ -156,7 +156,7 @@ export default function GradientPage() {
 
           {/* Preview */}
           <div className="space-y-6">
-            {gradient.length > 0 && (
+            {gradient && gradient.length > 0 && (
               <>
                 <div className="p-6 border rounded-lg bg-card">
                   <h2 className="text-xl font-semibold mb-4">Gradient Preview</h2>