fix(chart): improve error handling and color variety

- Add quotaExceeded flag to response for better error UX
- Show dedicated quota exceeded state with upgrade button
- Improve AI prompt to better detect data patterns
- Add chart type-specific colors (blue, indigo, emerald, violet, etc.)
- Replace generic primary/10 colors with varied accent colors

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

memento-note/lib/ai/services/chart-suggestion.service.ts

@@ -17,6 +17,7 @@ export interface SuggestChartsResponse {
   detectedData: string
   hasData: boolean
   error?: string
+  quotaExceeded?: boolean
 }
 
 export interface SuggestChartsRequest {
@@ -42,12 +43,16 @@ export async function suggestCharts(request: SuggestChartsRequest): Promise<Sugg
 
     if (!response.ok) {
       const errorData = await response.json().catch(() => ({ error: 'Unknown error' }))
+      const isQuotaError = response.status === 402 || errorData.error === 'QUOTA_EXCEEDED'
       return {
         suggestions: [],
         analyzedText: '',
         detectedData: '',
         hasData: false,
-        error: errorData.error || `HTTP ${response.status}`,
+        error: isQuotaError
+          ? 'AI quota exceeded. Please upgrade your plan to continue using AI features.'
+          : (errorData.error || `HTTP ${response.status}`),
+        quotaExceeded: isQuotaError,
       }
     }