fix: ship prebuilt lib and drop prepare for one-click git install

Avoids pnpm allowBuilds block on dsh plugin add; README install steps expanded for first-time users.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/format.d.ts

@@ -0,0 +1,3 @@
+export declare function escapeHtml(text: string): string;
+export declare function markdownToHtml(text: string): string;
+export declare function splitMessage(text: string, maxLength: number): string[];