Fix audit findings: budget editing, dead code, logging, multi-currency

- Add budget editing: updateBudget() API, edit button on budget cards,
  BudgetFormModal adapted for create/update (category locked on edit)
- Remove permanently-broken POST /auth/totp/verify stub and its unused
  TOTPVerifyRequest schema
- Wire getHoldingTransactions() to AssetDetail page — transaction history
  table now shows above the candlestick chart, sorted newest-first
- Fix multi-currency net worth in account_service: account balances are
  now converted to base_currency via ExchangeRate table before summing
- Replace silent bare pass exception handlers with logger.warning() in
  transactions.py (OCR/AI pipeline) and price_feed_service.py (search)
  — ValueError in date/number regex parsing left silent (control flow)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/auth.py

@@ -48,9 +48,6 @@ class TOTPSetupResponse(BaseModel):
     backup_codes: list[str]
 
 
-class TOTPVerifyRequest(BaseModel):
-    code: str
-
 
 class TOTPEnableRequest(BaseModel):
     secret: str