fix: token tracking pipeline + premium usage dashboard redesign

Backend fixes:
- Fix totalTokens defaulting to 0 when API omits totalTokenCount (now computes prompt+completion)
- Fix streaming metadata extraction: unwrap response wrapper in Anthropic/Gemini handlers
- Fix Zod schemas: handle SQL SUM(null) with nullable().transform()
- Add is_estimated column migration to token_usage table

Frontend redesign:
- Rewrite Usage page with area charts (nivo/line), horizontal bar model ranking
- StatCard: add trend indicators (% vs previous period) and inline SVG sparklines
- Premium color palette, prompt/completion ratio bar, top models mini-list
- Live indicator with 15s auto-refresh

Design system migration:
- Standardize all components on Gemini Nexus tokens (rounded-xl, border-white/[0.06])
- Refine UI components, proxy tabs, cloud account list, provider groups

src/ipc/database/cloudHandler.ts

@@ -153,6 +153,10 @@ export function ensureDatabaseInitialized(dbPath: string): void {
     if (!hasRequestType) {
       db.exec('ALTER TABLE token_usage ADD COLUMN request_type TEXT');
     }
+    const hasIsEstimated = tokenUsageTableInfo.some((col) => col.name === 'is_estimated');
+    if (!hasIsEstimated) {
+      db.exec('ALTER TABLE token_usage ADD COLUMN is_estimated INTEGER');
+    }
 
     // Create indexes for token_usage
     db.exec(`CREATE INDEX IF NOT EXISTS idx_token_usage_account ON token_usage(account_id);`);