Add tax features: summary report, deductible expenses, invoice tax fix, CSV export

- Add taxDeductible boolean to expenses schema + migration 0002
- Update expenses router, form, and list to support tax-deductible flag
- Fix invoice-view tax calculation (was hardcoded $0.00; now uses taxRate)
- New Tax Summary tab in Reports: year selector, income/deductions breakdown,
  SE tax + federal income estimates, quarterly bar chart
- CSV export for accountant with income + expense rows and tax summary

https://claude.ai/code/session_012sqEgNQpx676isepeoX4Mi

src/server/db/schema.ts

@@ -334,6 +334,7 @@ export const expenses = createTable(
     category: d.varchar({ length: 100 }),
     billable: d.boolean().default(false).notNull(),
     reimbursable: d.boolean().default(false).notNull(),
+    taxDeductible: d.boolean().default(false).notNull(),
     notes: d.varchar({ length: 500 }),
     createdById: d
       .varchar({ length: 255 })