feat(cli): TUI slash command parsing + local commands (P8-009) (#176)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

packages/cli/src/tui/commands/local/help.ts

@@ -0,0 +1,19 @@
+import type { ParsedCommand } from '@mosaic/types';
+import { commandRegistry } from '../registry.js';
+
+export function executeHelp(_parsed: ParsedCommand): string {
+  const commands = commandRegistry.getAll();
+  const lines = ['Available commands:', ''];
+
+  for (const cmd of commands) {
+    const aliases =
+      cmd.aliases.length > 0 ? ` (${cmd.aliases.map((a) => `/${a}`).join(', ')})` : '';
+    const argsStr =
+      cmd.args && cmd.args.length > 0
+        ? ' ' + cmd.args.map((a) => (a.optional ? `[${a.name}]` : `<${a.name}>`)).join(' ')
+        : '';
+    lines.push(`  /${cmd.name}${argsStr}${aliases} — ${cmd.description}`);
+  }
+
+  return lines.join('\n').trimEnd();
+}