Add context injection system (Milestone 3)

- Add src/core/context.ts with context gathering, ranking, and formatting
- Add src/core/config.ts for persistent configuration storage
- Add CLI commands: cortex context, cortex context-hook, cortex config
- Add memory_context MCP tool for Claude Code integration
- Add GET /api/context endpoint
- Include summary.ts from main branch for heartbeat dependency

src/mcp/index.ts

@@ -367,6 +367,37 @@ server.tool(
   }
 );
 
+// --- memory_context ---
+import { gatherContext, DEFAULT_CONTEXT_CONFIG } from '../core/context';
+
+server.tool(
+  'memory_context',
+  'Get relevant context for a Claude session. Gathers recent activity, project-specific nodes, open tasks, and decisions. Use at session start.',
+  {
+    project: z.string().optional().describe('Project name to filter by (e.g. "cortex")'),
+    query: z.string().optional().describe('Optional semantic search query'),
+    maxTokens: z.number().optional().describe(`Max tokens in output (default ${DEFAULT_CONTEXT_CONFIG.maxTokens})`),
+    maxNodes: z.number().optional().describe(`Max nodes to include (default ${DEFAULT_CONTEXT_CONFIG.maxNodes})`),
+  },
+  async ({ project, query: semanticQuery, maxTokens, maxNodes }) => {
+    const result = await gatherContext({
+      project,
+      semanticQuery,
+      config: {
+        maxTokens: maxTokens ?? DEFAULT_CONTEXT_CONFIG.maxTokens,
+        maxNodes: maxNodes ?? DEFAULT_CONTEXT_CONFIG.maxNodes,
+      },
+    });
+
+    return {
+      content: [{
+        type: 'text' as const,
+        text: result.formatted,
+      }],
+    };
+  }
+);
+
 // --- memory_summary ---
 import { getCachedSummary, generateSummary } from '../core/summary';