Standardize all playground pages on the interactive runtime

[Copilot]

Of 130 pages under playground/, only 31 used the working interactive template. The other 99 were broken in two distinct ways: 79 referenced a non-existent style.css/runtime.js (no styles → "single-row" layout, no execution), and 20 loaded playground-runtime.js but never created any .playground-block markup (light theme, non-interactive).

Changes

• tests/playground.test.ts — new conformance suite asserting every playground/*.html (except the landing page) loads playground-runtime.js, has a #playground-loading overlay, contains .playground-block / .playground-editor / .playground-run / .playground-output, uses the dark-theme CSS variables, and does not reference the legacy missing style.css or ./runtime.js.
• 98 playground pages converted to the standard template. A one-shot conversion extracted existing snippets from <pre>, <pre><code>, <div class="code-block">, and <textarea> containers and re-emitted each page with the canonical dark-theme styles, loading overlay, per-snippet .playground-block editors, and the shared <script type="module" src="playground-runtime.js">.
• Legacy code rewrites applied during conversion so snippets execute under the standard runtime (which only exposes tsb via import { … } from "tsb"):
  • const { X, Y } = tsb; → import { X, Y } from "tsb"; (anchored so destructuring like const { codes } = tsb.factorize(...) is left for the next rule)
  • tsb.foo(...) → collect referenced names, prepend a single import { foo, … } from "tsb";, strip the tsb. prefix
• Fallback for pages with no extractable snippets (UI-builder pages such as date_range.html, timestamp.html, benchmarks.html): seed a starter .playground-block with imports/constructors discovered in the page's own scripts, keeping the page interactive.

The conformance test now covers all 130 pages with 1162 assertions; running it with the previous content surfaced 666 failures across the broken pages, which is the regression guard going forward.