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/parse.ts

@@ -0,0 +1,11 @@
+import type { ParsedCommand } from '@mosaic/types';
+
+export function parseSlashCommand(input: string): ParsedCommand | null {
+  const match = input.match(/^\/([a-z][a-z0-9:_-]*)\s*(.*)?$/i);
+  if (!match) return null;
+  return {
+    command: match[1]!,
+    args: match[2]?.trim() || null,
+    raw: input,
+  };
+}