Wrap naked expressions in playground blocks with console.log()

[Copilot]

Most playground tutorial blocks ended in bare expression statements (e.g. seriesAdd(a, b).values; // [5, 7, 9]) or const result = …; with the value documented only in a trailing comment. Since the playground runtime captures output exclusively from console.log/warn/error, clicking ▶ Run displayed (no output — add console.log() to see results) instead of demonstrating behavior. Audit found 425 of 770 blocks affected.

Changes

• Wrap single-line expression statements in console.log(...), preserving indentation and inline // expected comments.
• Append console.log(<lastVar>); to blocks whose only meaningful output is bound to a top-level const/let/var.
• Skip non-runnable content: Python comparison snippets (import pandas, pd./np., print(, # end-of-line comments), TS type/signature reference lines (e.g. df.assign(spec: AssignSpec): DataFrame;), method-chain continuation lines (.toHtml();), multi-line statements (tracked via paren/brace/bracket depth), assignments (with HTML-entity decoding so => is recognized as =>), and placeholder blocks.

321 blocks across 70 playground/*.html files updated. Each block's TypeScript was transpiled before and after to confirm no new syntax errors.

Example

 import { Series, seriesAdd, seriesMul } from "tsb";

 const s = new Series({ data: [1, null, NaN, 4] });
-seriesAdd(s, 10).values;  // [11, null, NaN, 14]
-seriesMul(s, 2).values;   // [2, null, NaN, 8]
+console.log(seriesAdd(s, 10).values);  // [11, null, NaN, 14]
+console.log(seriesMul(s, 2).values);   // [2, null, NaN, 8]

 const df2 = dataFrameAssign(df, {
   c: [7, 8, 9],
   d: new Series({ data: [4, 5, 6] }),
 });
 // df2.columns.values  →  ["a", "b", "c", "d"]
+console.log(df2);

Not addressed

A handful of blocks remain output-less by design or due to pre-existing bugs unrelated to logging — pure interface/type declarations, comment-only snippets, and broken placeholders like Click ▶ Run to execute in crosstab.html/datetime_tz.html/factorize.html/get_dummies.html/str_get_dummies.html. Those warrant separate fixes.