chore(deps): drop unused cupertino_icons + tslib

Both verified unused at the source/config level (Fable #461 +
audit note #460):

- cupertino_icons: zero `CupertinoIcons` / cupertino imports in
  flutter_client/lib/. Pure `flutter create` template residue;
  the design system mandates Lucide.
- tslib: web/tsconfig.json does not set `importHelpers: true`,
  so TypeScript inlines helpers per-file. Declared peer with no
  runtime consumer.

`npm uninstall tslib --save-dev` updated package-lock.json
surgically (8 lines removed for the tslib entry only). No other
deps disturbed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/package.json

@@ -24,7 +24,6 @@
     "svelte": "^5.1.9",
     "svelte-check": "^4.0.5",
     "tailwindcss": "^3.4.14",
-    "tslib": "^2.8.0",
     "typescript": "^5.6.3",
     "vite": "^5.4.10",
     "vitest": "^2.1.4"