Investment portfolio charts, search fix, and holding creation fixes

- Add four portfolio charts: allocation donut by holding, allocation
  donut by asset type, cost basis vs current value bar, return % bar
- Fix asset search to use yf.Search() full-text instead of ticker-only
  lookup — name searches like "vanguard ftse all world" now work
- Fix holding creation double-quantity bug: holdings now created with
  quantity=0 so buy transaction is sole source of quantity/cost basis
- Add per-share / total price toggle in Add Holding modal with live
  calculated equivalent shown as you type
- Add ErrorBoundary in AppShell so render errors show a message instead
  of a blank page
- Fix donut charts using || instead of ?? when falling back from
  current_value to cost_basis_total (0 was not falling through ??)
- Allow HoldingCreate.quantity >= 0 (was gt=0) to support zero-init
- Fix error display for Pydantic v2 array-of-objects validation errors

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

README.md

@@ -26,12 +26,13 @@ Runs entirely on your own hardware via Docker Compose. Designed for LAN access w
 
 ### Investments
 - Portfolio tracking with holdings and buy/sell/dividend/split transactions
+- Asset search by name or ticker (stocks, ETFs, crypto, funds) via **yfinance** full-text search
 - Live price feeds: stocks and ETFs via **yfinance**, crypto via **CoinGecko** (refreshed every 15 minutes)
 - Hourly FX rates for multi-currency conversion to GBP base
 - TWRR and MWRR performance metrics
 - Capital gains reporting (short/long-term by tax year)
 - OHLCV candlestick charts per asset
-- Allocation treemap across the full portfolio
+- Portfolio visualisations: allocation donut by holding, allocation donut by asset type, cost basis vs current value bar chart, return % per holding bar chart
 
 ### Reports
 Seven report views: