feat(trading-signals-vocs): add Vocs documentation site with interactive demos and backtesting

[bennycode]

Part of #1288.

This adds a new trading-signals-vocs package: a documentation site built on Vocs 2 (the framework behind the XMTP docs referenced in the ticket), with full feature parity to the current Next.js site plus docs-native extras. It runs alongside trading-signals-docs for now — swapping the deployment is a follow-up.

What's in the site

• 127 indicator pages across trend, momentum, volatility, and volume — generated from the existing demo registry (npm run generate). Each page has a live Highcharts demo (dataset pills incl. custom candle JSON upload, price chart, collapsible sample values) and a Twoslash-checked usage snippet: class name and constructor args are extracted from each demo's createIndicator, and a wrong snippet fails the build.
• Utility function playgrounds and the full in-browser backtester (all strategies, protection modal, config reference, buy-and-hold baseline) on a full-width page.
• Welcome page with a mermaid architecture diagram and package overview cards.
• Hand-written indicator intros live in src/intros/<category>/<id>.md and survive regeneration (RMI has one as an example).
• Free extras from Vocs: full-text search, dark mode, hover type popups from the local trading-signals build, llms.txt/llms-full.txt, per-page "Copy for AI".

Engineering notes

• @typedtrader/exchange/schemas subpath (first commit): CandleSchema/CandleBaseSchema moved to a zod-only module so browser bundles can validate uploaded candles without dragging broker code (Node built-ins) into the client graph. The barrel re-exports everything, so existing consumers are unaffected — exchange tests, dependent typechecks, and knip are green.
• Node built-in shims: the Vocs CLI passes configFile: false, so scripts/site.ts wraps the same Vite invocation with a small plugin that shims node:events/node:crypto/node:assert/node:util in the client environment only. That is what lets trading-strategies and AlpacaBrokerMock run the backtester in the browser.
• Twoslash vs TypeScript 7: the repo's TS 7 has no JS compiler API and ships no lib.*.d.ts, so the package pins a local typescript@^5.9 and points Twoslash at its lib directory in vocs.config.ts.
• waku pinned to 1.0.0-beta.6 via a root override: beta.9 satisfies vocs' peer range but breaks its router at runtime (blank pages).

Verification

Built statically (267 files) and clicked through in Chrome in both themes: indicator demos incl. custom renders (MACD, QQE, Ichimoku), candle JSON upload, and a full backtest run (buy-and-hold on Synthetic Uptrend, +32.49% ROI with baseline comparison). oxlint, tsc, and knip are green across the repo.

Not ported yet (intentionally): Playwright e2e specs and deployment wiring — those belong to the actual site swap.