feat: Update Step 7 with tool-based AI + Fix auth callback

Step 7 Updates (AI Chat with Structured Output):
- Created lib/ai-schemas.ts with Zod schema for NodeSuggestion
- Updated app/api/chat/route.ts:
  - Changed import from 'ai' to '@ai-sdk/react' for streamText
  - Added tools configuration with 'suggest_node' tool using NodeSuggestionSchema
  - Added persona support with dynamic system prompts
  - Extracts persona from request data object
- Rewrote app/chat/page.tsx:
  - Changed from server component to client component ('use client')
  - Uses useChat from '@ai-sdk/react' (fixes broken 'ai/react' import)
  - Added experimental_onToolCall handler for node suggestions
  - Redirects to /editor/new with AI-generated title/body as query params
  - Integrated MicrophoneRecorder for voice input
  - Added persona support (currently hardcoded to 'Socratic')
- Added tests/magnitude/07-chat.mag.ts with tests for:
  - Basic chat functionality
  - AI-triggered node suggestions with redirect to editor

Auth Callback Fixes:
- Fixed app/api/auth/callback/route.ts:
  - Changed to use agent.api.com.atproto.server.getSession() to fetch session
  - Previously used agent.getSession() which returned empty did/handle
  - Added user upsert to SurrealDB (INSERT...ON DUPLICATE KEY UPDATE)
  - Fixed variable references (session.did -> did, session.handle -> handle)
  - Properly creates user record before minting JWT

CLAUDE.md Updates:
- Added git commit HEREDOC syntax documentation for proper quote escaping
- Clarified that this project allows direct git commits (no PGP signatures)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/ai-schemas.ts

@@ -0,0 +1,19 @@
+import { z } from 'zod';
+
+/**
+ * This Zod schema defines the *only* structured output
+ * we want the AI to be able to generate. We will pass
+ * this to the Vercel AI SDK to guarantee the AI's output
+ * conforms to this shape.
+ */
+export const NodeSuggestionSchema = z.object({
+  action: z.literal('suggest_node'),
+  title: z
+    .string()
+    .describe('A concise, descriptive title for the thought node.'),
+  body: z
+    .string()
+    .describe('The full, well-structured content of the thought node.'),
+});
+
+export type NodeSuggestion = z.infer<typeof NodeSuggestionSchema>;