feat: add structured content extraction and batch embedding optimization to highlight()

Fix highlight() hanging on structured text input by addressing 3 root causes:

1. embedBatch() now uses native WASM batch API (single forward pass instead
   of N individual embed() calls via Promise.all)

2. highlight() auto-detects content type (plain text, rich-text JSON, HTML,
   Markdown) and extracts meaningful text segments. Supports TipTap, Slate.js,
   Lexical, Draft.js, and Quill Delta formats. New contentType hint and
   contentExtractor callback for custom parsers.

3. Semantic matching phase has 10s timeout - falls back to text-only matches
   instead of hanging indefinitely.

Also fixes extractTextContent() array check: uses type-based detection
(typeof data[0] === 'number') instead of length-based (data.length > 10)
so arrays of objects are properly indexed for text search.

New types: ContentType, ContentCategory, ExtractedSegment
New fields: HighlightParams.contentType, HighlightParams.contentExtractor,
            Highlight.contentCategory

docs/api/README.md

@@ -270,41 +270,85 @@ results[0].matchSource     // 'both' | 'text' | 'semantic'
 
 ---
 
-### `highlight(params)` → `Promise<Highlight[]>` ✨ *New v7.8.0*
+### `highlight(params)` → `Promise<Highlight[]>` ✨ *New v7.8.0, Enhanced v7.9.0*
 
 Zero-config highlighting for both exact matches AND semantic concepts.
+Handles plain text, rich-text JSON (TipTap, Slate, Lexical, Draft.js, Quill), HTML, and Markdown automatically.
 
 ```typescript
+// Plain text (works as before)
 const highlights = await brain.highlight({
   query: "david the warrior",
   text: "David Smith is a brave fighter who battles dragons"
 })
-
-// Returns both text matches AND semantic matches:
 // [
 //   { text: "David", score: 1.0, position: [0, 5], matchType: 'text' },
 //   { text: "fighter", score: 0.78, position: [25, 32], matchType: 'semantic' },
 //   { text: "battles", score: 0.72, position: [37, 44], matchType: 'semantic' }
 // ]
+
+// Rich-text JSON (auto-detected, v7.9.0)
+const highlights = await brain.highlight({
+  query: "david the warrior",
+  text: JSON.stringify(tiptapDocument)  // TipTap, Slate, Lexical, Draft.js, Quill
+})
+// Extracts text from nodes, annotates with contentCategory:
+// [
+//   { text: "David", score: 1.0, matchType: 'text', contentCategory: 'heading' },
+//   { text: "fighter", score: 0.78, matchType: 'semantic', contentCategory: 'prose' }
+// ]
+
+// HTML input (auto-detected, v7.9.0)
+const highlights = await brain.highlight({
+  query: "warrior",
+  text: "<h1>David the Warrior</h1><p>A brave fighter.</p>"
+})
+
+// Custom extractor for proprietary formats (v7.9.0)
+const highlights = await brain.highlight({
+  query: "function",
+  text: sourceCode,
+  contentExtractor: (text) => treeSitterParse(text)  // Your custom parser
+})
 ```
 
 **Parameters:**
 - `query`: `string` - The search query
-- `text`: `string` - Text to highlight (e.g., entity.data)
+- `text`: `string` - Text to highlight (plain text, JSON, HTML, or Markdown)
 - `granularity?`: `'word' | 'phrase' | 'sentence'` - Highlight unit (default: 'word')
 - `threshold?`: `number` - Min similarity for semantic matches (default: 0.5)
+- `contentType?`: `ContentType` - Optional hint: `'plaintext' | 'richtext-json' | 'html' | 'markdown'`. Skips auto-detection when provided. *(v7.9.0)*
+- `contentExtractor?`: `(text: string) => ExtractedSegment[]` - Custom parser. Bypasses built-in detection entirely. *(v7.9.0)*
 
 **Returns:** `Promise<Highlight[]>`
 - `text` - The matched text
 - `score` - Match score (1.0 for text matches, varies for semantic)
-- `position` - [start, end] indices in original text
+- `position` - [start, end] indices in extracted text
 - `matchType` - `'text'` (exact) or `'semantic'` (concept)
+- `contentCategory?` - `'prose' | 'heading' | 'code' | 'label'` — Role of the source text in the document. Present when input is structured. *(v7.9.0)*
+
+**Supported Rich-Text Formats (v7.9.0):**
+
+| Format | Detection | Text nodes |
+|--------|-----------|------------|
+| TipTap / ProseMirror | `{ type: 'doc', content: [...] }` | `{ type: 'text', text }` |
+| Slate.js | `[{ type, children }]` | `{ text }` |
+| Lexical | `{ root: { children } }` | `{ type: 'text', text }` |
+| Draft.js | `{ blocks: [{ text }] }` | `{ text }` in block |
+| Quill Delta | `{ ops: [{ insert }] }` | `{ insert }` |
+| HTML | Tags like `<h1>`, `<p>`, `<code>` | Visible text content |
+| Markdown | `#` headings, ` ``` ` code blocks | Stripped markup |
+
+**Timeout Protection (v7.9.0):**
+Semantic matching has a 10-second timeout. If embedding takes too long (e.g., WASM stall), `highlight()` returns text-only matches instead of hanging.
 
 **UI Pattern:**
 ```typescript
-// Style differently based on match type
+// Style differently based on match type and content category
 highlights.forEach(h => {
   const style = h.matchType === 'text' ? 'font-weight: bold' : 'background: yellow'
+  if (h.contentCategory === 'heading') { /* render as heading highlight */ }
+  if (h.contentCategory === 'code') { /* render with code styling */ }
   // Apply style from h.position[0] to h.position[1]
 })
 ```
@@ -1677,9 +1721,9 @@ console.log(vector.length) // 384
 
 ---
 
-### `embedBatch(texts)` → `Promise<number[][]>` ✨ *New v7.1.0*
+### `embedBatch(texts)` → `Promise<number[][]>` ✨ *New v7.1.0, Optimized v7.9.0*
 
-Batch embed multiple texts efficiently.
+Batch embed multiple texts using native WASM batch API (single forward pass).
 
 ```typescript
 const embeddings = await brain.embedBatch([
@@ -1691,6 +1735,8 @@ console.log(embeddings.length)    // 3
 console.log(embeddings[0].length) // 384
 ```
 
+> **v7.9.0**: Now uses the WASM engine's native `embed_batch()` for a single model forward pass instead of N individual calls. This is the same batch API used internally by `highlight()`.
+
 ---
 
 ### `similarity(textA, textB)` → `Promise<number>` ✨ *New v7.1.0*