Add structured sections and hierarchical navigation

Add --section flag to add/update commands for structured node content,
render sections and inline children in show, and add memory children command.

src/cli/commands/children.ts

@@ -0,0 +1,45 @@
+import { Command } from 'commander';
+import chalk from 'chalk';
+import { findNodeByPrefix } from '../../core/store';
+import { getConnections } from '../../core/graph';
+import { NodeKind } from '../../types';
+
+export const childrenCommand = new Command('children')
+  .argument('<id>', 'Parent node ID (or prefix)')
+  .option('--kind <kind>', 'Filter children by kind')
+  .option('--format <fmt>', 'Output format: text or json', 'text')
+  .description('List child nodes (outgoing "contains" edges)')
+  .action(async (idRaw: string, opts) => {
+    const node = findNodeByPrefix(idRaw);
+    if (!node) {
+      console.error(chalk.red(`Node not found: ${idRaw}`));
+      process.exit(1);
+    }
+
+    const conns = getConnections(node.id);
+    let children = conns.outgoing.filter(c => c.type === 'contains');
+
+    if (opts.kind) {
+      children = children.filter(c => c.node.kind === opts.kind);
+    }
+
+    if (opts.format === 'json') {
+      console.log(JSON.stringify(children.map(c => ({
+        id: c.node.id,
+        kind: c.node.kind,
+        title: c.node.title,
+        status: c.node.status,
+      })), null, 2));
+      return;
+    }
+
+    if (children.length === 0) {
+      console.log(chalk.dim('No children.'));
+      return;
+    }
+
+    console.log(chalk.bold(`Children of [${node.kind}] ${node.title}:`));
+    for (const c of children) {
+      console.log(`  ${c.node.id.slice(0, 8)} [${c.node.kind}] ${c.node.title}`);
+    }
+  });