Add service worker implementation and tests for PWA caching strategy

- Implemented a service worker (sw.js) that handles installation, activation, and fetch events.
- Added caching logic for public assets and a fallback for offline navigation.
- Created unit tests (sw.test.ts) to validate service worker behavior, including asset caching, navigation handling, and activation logic.
- Ensured that private API routes and third-party requests are excluded from caching.

src/components/design-system/PageLayout.tsx

@@ -2,6 +2,7 @@ import type { ReactNode } from "react";
 import { Link } from "react-router";
 import { ThemeControl } from "../ThemeProvider";
 import { Button } from "./primitives";
+import { InstallApp, PwaStatus } from "../PwaControls";
 
 /** The existing design-system page shell, shared without page-specific styling. */
 export function PageLayout({
@@ -34,10 +35,12 @@ export function PageLayout({
         <div className="ds-header-actions">{header}<ThemeControl /></div>
       </header>
       <main id={mainId} className="ds-main" tabIndex={-1}>
+        <PwaStatus />
         {children}
         <footer className="ds-footer">
           <span className="ds-wordmark">Mina Habits.</span>
           <span>A little, every day.</span>
+          <InstallApp />
           <Button
             variant="text"
             onClick={() => window.scrollTo({ top: 0, behavior: "instant" })}