feat(ai): search + read grounding tools

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/ai/agent/tools/read.js

@@ -0,0 +1,23 @@
+import { pool } from '../../../db/pool.js';
+
+const TABLE = { page: 'pages', ref: 'refs', task: 'tasks', conversation: 'conversations' };
+
+export const readTool = {
+  name: 'read',
+  description: 'Read a single entity (page, ref, task, conversation) by id for grounding.',
+  input_schema: {
+    type: 'object',
+    properties: {
+      kind: { type: 'string', enum: ['page', 'ref', 'task', 'conversation'] },
+      id: { type: 'string', description: 'uuid of the entity' }
+    },
+    required: ['kind', 'id']
+  },
+  async handler({ kind, id }, _ctx) {
+    const table = TABLE[kind];
+    if (!table) return { error: `unknown kind "${kind}"` };
+    const { rows: [row] } = await pool.query(`SELECT * FROM ${table} WHERE id=$1`, [id]);
+    if (!row) return { error: `${kind} ${id} not found` };
+    return row;
+  }
+};