feat: TypeScript installation wizard with @clack/prompts TUI (#1)

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

src/stages/welcome.ts

@@ -0,0 +1,18 @@
+import type { WizardPrompter } from '../prompter/interface.js';
+import type { WizardState } from '../types.js';
+import { VERSION } from '../constants.js';
+
+export async function welcomeStage(
+  p: WizardPrompter,
+  _state: WizardState,
+): Promise<void> {
+  p.intro(`Mosaic Installation Wizard v${VERSION}`);
+  p.note(
+    `Mosaic is an agent framework that gives AI coding assistants\n` +
+      `a persistent identity, shared skills, and structured workflows.\n\n` +
+      `It works with Claude Code, Codex, and OpenCode.\n\n` +
+      `All config is stored locally in ~/.config/mosaic/.\n` +
+      `No data is sent anywhere. No accounts required.`,
+    'What is Mosaic?',
+  );
+}