Switch from Langbase to runllm (#1339)

This PR uses RunLLM as the Doc asssistant

## Pull Request approval

You will need to get your PR approved by at least one member of the
Sourcegraph team. For reviews of docs formatting, styles, and component
usage, please tag the docs team via the #docs Slack channel.

---------

Co-authored-by: Amp <[email protected]>

Author: mibali

AGENTS.md

@@ -0,0 +1,54 @@
+# Sourcegraph Docs - Agent Instructions
+
+## Build Commands
+
+- **Type Check**: `npx tsc --noEmit`
+- **Build**: `npm run build` 
+- **Dev**: `npm run dev`
+- **Lint**: `npm run lint`
+
+## AI Chat Integration
+
+This site uses **runLLM** for the AI chat widget. The integration is implemented via:
+
+- **Location**: `src/app/layout.tsx`
+- **Widget**: runLLM script loaded via Next.js `<Script>` component
+- **Configuration**: 
+  - Position: BOTTOM_RIGHT
+  - Theme color: #FF5543 (Sourcegraph brand color)
+  - Button text: "Ask AI"
+  - Keyboard shortcut: Mod+j
+
+### runLLM Configuration
+
+To update the runLLM assistant ID or other settings, modify the Script component in `src/app/layout.tsx`:
+
+```tsx
+<Script
+  id="runllm-widget-script"
+  type="module"
+  src="https://widget.runllm.com"
+  crossOrigin=""
+  runllm-keyboard-shortcut="Mod+j"
+  runllm-name="Sourcegraph AI Assistant"
+  runllm-position="BOTTOM_RIGHT"
+  runllm-assistant-id="YOUR_ASSISTANT_ID"  // Update this
+  runllm-theme-color="#FF5543"
+  runllm-floating-button-text="Ask AI"
+  async
+/>
+```
+
+### Previous Integration
+
+Previously used **Langbase** with custom React components. This has been completely removed:
+- Removed `@langbase/components` and `langbase` packages
+- Removed custom chat components (`src/app/chat.tsx`, `src/components/ChatBot/`)
+- Removed API routes (`src/app/api/chat/`)
+- Removed memory creation scripts
+
+## Important Notes
+
+- **Assistant ID**: The `runllm-assistant-id` is currently set to "YOUR_ASSISTANT_ID" and needs to be updated with the actual Sourcegraph runLLM assistant ID
+- **Deployment**: After updating the assistant ID, add the deployment URL to the runLLM dashboard
+- **Styling**: The widget inherits the site's theme and uses the Sourcegraph brand color (#FF5543)