Add real-world examples section to the playground

[Copilot]

The playground had a page per individual feature but nothing showing tsb used end-to-end on realistic data. This adds an Examples section: 10 self-contained, in-browser tutorials covering common pandas workflows.

Hub

• playground/examples.html — grid of 10 example cards.
• playground/index.html — new "Real-World Examples" section above the feature roadmap, linking to the hub.

Examples (playground/example_*.html)

Each page has 1–3 editable code blocks with inline realistic data, a Python equivalent tab, and ASCII bar-chart output rendered through console.log.

Example	Domain	APIs exercised
💰 Sales Dashboard	Retail analytics	readCsv, groupby().agg, nlargestDataFrame
📈 Stock Returns	Finance	pctChangeSeries, Series.rolling().mean/std, SMA crossover
🌦️ Weather Trends	Climate	dt accessor, groupby
👥 Customer Cohorts	SaaS growth	groupby().size, cumsum, pctChangeSeries
📊 Survey Cross-tabs	Research	crosstab with normalize: "index"
🪵 Server Log Analysis	DevOps	Series.map, groupby, pivot, fillna
🧪 A/B Test Results	Experimentation	groupby().agg, lift, describe
🌐 Web Analytics Pivot	Marketing	pivotTable (source × device)
⚽ Sports Standings	Sports analytics	concat, groupby, rankSeries, sortValues
🏷️ Pricing Buckets	E-commerce	cut with labels, valueCounts

All pages reuse the existing playground-runtime.js (TS-compiler + tsb bundle + transparent-textarea highlighting) — no runtime changes.

Charts

Examples render visual output by emitting unicode block bars through console.log, which the runtime captures and shows in the output panel:

function chart(title: string, rows: Array<[string, number]>): void {
  const max = Math.max(...rows.map(r => r[1]));
  console.log(title);
  for (const [label, value] of rows) {
    const len = Math.round((value / max) * 28);
    console.log(label.padEnd(14) + " | " + "█".repeat(len) + " " + value.toFixed(2));
  }
}

Verification

A Playwright harness loads all 11 new pages, clicks every Run button, and asserts every block runs without error and produces output (22/22 blocks pass). The examples use only existing public tsb APIs; no src/ changes.