Add Stationery and Stationery Dark themes with notebook chrome.

Manila folders, ruled chat, post-it nav, and folder tabs; dark variant uses Catppuccin Mocha colors with muted stickies and soft glows.

src/app/utils/paperSafeInk.ts

@@ -0,0 +1,2 @@
+/** Stationery paper ink for display names (follows --stationery-ink) */
+export const STATIONERY_NAME_INK = 'var(--stationery-ink)';