Add webview widget for embedded web browser in project dashboards

New widget type that renders any URL (local dev servers, HTML reports)
directly in the dashboard via WKWebView. Sections with webviews
automatically split layout: grid widgets left, webview right.
Configurable height, non-persistent data store, navigation error logging.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scarf/docs/DASHBOARD_SCHEMA.md

@@ -141,13 +141,29 @@ Create `.scarf/dashboard.json` in your project root:
 
 - `status`: "done" (checkmark), "active" (filled circle), "pending" (empty circle)
 
+### webview — Embedded web browser
+
+```json
+{
+  "type": "webview",
+  "title": "Project Dashboard",
+  "url": "http://localhost:8000",
+  "height": 500
+}
+```
+
+- `url`: Any URL — local servers, file paths, or remote pages
+- `height`: Height in points (optional, default: 400)
+
+When a section contains a webview alongside other widgets, Scarf splits the layout automatically: grid widgets on the left, webview on the right. If the section contains only a webview, it uses the full width.
+
 ## Agent Instructions
 
 To have your Hermes agent generate a dashboard, include these instructions:
 
 > Analyze the project and create a `.scarf/dashboard.json` file with relevant metrics,
 > status indicators, and visualizations. Use the Scarf dashboard schema with sections
-> containing stat, progress, text, table, chart, and list widgets. Register the project
+> containing stat, progress, text, table, chart, list, and webview widgets. Register the project
 > in `~/.hermes/scarf/projects.json` if not already registered.
 
 The agent can update the dashboard file at any time — Scarf watches for changes and re-renders automatically.