CoinGecko and Messari records carry no stablecoin tags, so the classifier
labels them 'Other'. Their higher source priority let that 'Other' beat
DeFiLlama's 'Stablecoin' for every coin CMC does not list, dropping those
coins from stablecoin totals. The merge now takes the highest-priority
concrete category and falls back to 'Other' only when no source has one.

With the mock data this restores 43 coins (USDTB, USDX, crvUSD, BOLD, ...)
and $4.43B of market cap to the stablecoin totals.

The 9 failing AssetClassifier suites had failed since they were added in
a8a43b2; 75b0bf6 did not touch the classifier.

Code fixes
- classify() returned null for null/string tags and threw on non-string
  symbols (_createAssetKey); it now treats non-array tags as no tags and
  keys on normalized values. Fetchers dereference the result directly.
- Honor DeFiLlama pegType on the asset (peggedUSD -> Stablecoin/USD),
  ahead of tags, as the fetcher already does.
- With no tags array at all, a fiat stablecoin ticker (USDT, EURC) is a
  Stablecoin. Fetchers always pass an array, so production is unaffected.
- Detect peg from decorated tickers: USDC.e, ibc/USDC, USDC(Wormhole),
  vBUSD, axlUSDC, lisUSD, USDe, USD1, limited to currencies with known
  stablecoins so STND does not read as STN.
- Add DAI, UST, USTC aliases (USD).

Test fixes
- ChainSpecificClassification: stray closing brace and the pre-a8a43b2
  classify(asset) signature.
- PerformanceStress: assertions moved out of the timed loop; 20k jest
  expect() calls took ~400ms of the 100ms budget.
- ComplexSymbolPatterns: U/"USD Coin Short", E/"EUR Coin Short" and
  USSS/"Triple S USD" expected null, contradicting the name-based
  detection the same suite requires for "Double U EUR" and "Dollar Symbol".

Add a head partial with a dark color-scheme meta and an inline
html/body background matching --bg-body, included in every page's
<head> ahead of common.css. The first frame is now navy instead of
the browser's default white while common.css and its imports
(design-system.css, components.css) are still loading, such as on a
cold-cache navigation from a site that embeds StablecoinWatch.