Add interactive playground with live TypeScript execution

biome.json

@@ -7,7 +7,7 @@
   },
   "files": {
     "ignoreUnknown": false,
-    "ignore": ["dist/**", "node_modules/**", "*.d.ts"]
+    "ignore": ["dist/**", "node_modules/**", "*.d.ts", "playground/**/*.js"]
   },
   "formatter": {
     "enabled": true,

docs/playground.md

@@ -0,0 +1,127 @@
+# Playground Pages — Design & Requirements
+
+Every feature in **tsb** ships with an interactive playground page hosted on
+GitHub Pages. This document describes the required properties that every
+playground page must satisfy.
+
+## Required Properties
+
+### 1. Executable Code Blocks
+
+Each code example on a playground page **must** be executable in the browser.
+Users can edit the code, click **▶ Run** (or press **Ctrl+Enter**), and see
+real output rendered below the editor.
+
+- Use `<textarea class="playground-editor">` for the editable code area.
+- Wrap each example in a `<div class="playground-block">` container.
+- Provide **▶ Run** and **↺ Reset** buttons in a `.playground-header`.
+- Display results in a `<div class="playground-output">`.
+
+### 2. Full TypeScript Support
+
+Code blocks accept TypeScript. The playground runtime loads the TypeScript
+compiler from CDN and transpiles user code to JavaScript before execution.
+Users can write type annotations, interfaces, and generics — the compiler
+strips them automatically.
+
+- TypeScript compiler: loaded from `https://cdn.jsdelivr.net/npm/typescript@5/lib/typescript.js`
+- No WASM required — the compiler runs natively in JavaScript.
+
+### 3. Live tsb Library Access
+
+The full tsb API is available in every code block. Users import from `"tsb"`
+exactly as they would in a real project:
+
+```typescript
+import { Index, Series, Dtype } from "tsb";
+```
+
+The playground runtime transforms these imports to reference the browser
+bundle built by CI (`playground/dist/index.js`).
+
+### 4. Output Capture
+
+All `console.log()`, `console.error()`, and `console.warn()` output is
+intercepted and rendered in the output area. tsb objects (Index, Series, etc.)
+display their human-readable `toString()` representation.
+
+### 5. Dark Theme
+
+Pages use the project's standard dark GitHub-inspired theme (CSS variables
+`--bg`, `--surface`, `--border`, `--text`, `--accent`, `--green`). See
+`playground/index-playground.html` for the canonical style definitions.
+
+### 6. Loading State
+
+A loading overlay with a spinner is shown while the TypeScript compiler and
+tsb bundle are fetched. All Run buttons are disabled until initialization
+completes, preventing premature execution.
+
+### 7. Keyboard Shortcuts
+
+- **Ctrl+Enter** (or **Cmd+Enter** on macOS): Run the current code block.
+- **Tab**: Insert two spaces (does not move focus).
+
+### 8. Reset Support
+
+Every code block has a **↺ Reset** button that restores the original example
+code and clears the output.
+
+### 9. Free-form Scratch Pad
+
+Each playground page should include a final "Try It Yourself" section with an
+empty (or lightly seeded) code block where users can experiment freely.
+
+## Architecture
+
+```
+playground/
+  index.html                 ← Landing page / feature roadmap
+  index-playground.html      ← Index & RangeIndex interactive tutorial
+  playground-runtime.js      ← Shared runtime (TS transpilation + execution)
+  dist/                      ← Built by CI (bun build, not committed)
+    index.js                 ← tsb browser bundle (ESM)
+```
+
+### Runtime Flow
+
+1. The HTML page loads `playground-runtime.js` as an ES module.
+2. The runtime imports the tsb bundle from `./dist/index.js` and stores it
+   on `window.__tsb`.
+3. The TypeScript compiler is loaded from CDN via a dynamic `<script>` tag.
+4. Each `.playground-block` is initialized with event listeners for Run,
+   Reset, Tab, and Ctrl+Enter.
+5. On **Run**:
+   - `import { … } from "tsb"` is rewritten to `const { … } = window.__tsb;`
+   - The TypeScript compiler transpiles the code to JavaScript.
+   - The JavaScript is executed via `new Function()` with console output
+     captured and displayed.
+
+### Adding a New Playground Page
+
+1. Create `playground/{feature}.html` following the template in
+   `index-playground.html`.
+2. Include the runtime: `<script type="module" src="playground-runtime.js"></script>`
+3. Add the loading overlay (`#playground-loading`).
+4. Structure examples as `.playground-block` containers with `.playground-editor`,
+   `.playground-run`, `.playground-reset`, and `.playground-output` elements.
+5. End with a "Try It Yourself" scratch pad.
+6. Link the page from `playground/index.html`.
+
+### Building the Bundle Locally
+
+```bash
+bun build ./src/index.ts --outdir ./playground/dist --target browser --minify
+```
+
+The CI pipeline (`pages.yml`) runs this automatically during deployment.
+
+## Non-Goals (Current Scope)
+
+- **Syntax highlighting** in the editor: the current implementation uses a
+  plain `<textarea>`. A future enhancement could integrate CodeMirror or
+  Monaco for richer editing.
+- **Infinite loop protection**: long-running or infinite loops will hang the
+  browser tab. A Web Worker–based sandbox could be added later.
+- **Type checking**: the playground transpiles but does not type-check.
+  Adding diagnostics display is a potential future enhancement.