Clear offline data on logout, test offline plan and recipe reads, drop Pillow

- POST /auth/logout answers with Clear-Site-Data: "storage", "cache", which
  removes the verified-session marker, the service worker and its caches, so
  an offline visit after logout cannot reopen household data. The 401/403
  clearing path is unchanged.
- The service worker no longer answers network-only requests; it leaves them
  to the browser. Chrome stalls a Clear-Site-Data navigation that the worker
  answered, so the logout POST must bypass it.
- New tests send plan and recipe reads through the real API client and the
  real network-first strategy online, then serve them from the cache offline.
- The icon generator is now Go on golang.org/x/image (approved) instead of
  Python on Pillow; the icons are regenerated with it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/sw/worker.test.ts

@@ -1,7 +1,7 @@
 // The service worker itself needs worker globals, so these tests read its
 // source: they pin the parts routes.ts cannot express — the API cache's
-// strategy, the font strategy's expiration and the font route's place ahead of
-// the precache route.
+// strategy, the font strategy's expiration, the font route's place ahead of
+// the precache route and network-only requests left to the browser.
 import { describe, expect, it } from 'vitest'
 import source from '../sw.ts?raw'
 
@@ -27,6 +27,16 @@ describe('service worker source', () => {
     expect(precache).toBeGreaterThan(fontRoute)
   })
 
+  it('leaves network-only requests to the browser instead of answering them', () => {
+    // Chrome stalls a navigation whose Clear-Site-Data response (POST
+    // /auth/logout) the worker answered, so the worker must not match it.
+    expect(source).toMatch(
+      /function answered\(options: \{ request: Request; url: URL \}\): boolean \{\s*return routeOf\(options\)\.strategy !== 'network-only'/,
+    )
+    expect(source).toContain('registerRoute(answered, handle, method)')
+    expect(source).not.toContain('registerRoute(() => true')
+  })
+
   it('activates a waiting worker when the update prompt sends SKIP_WAITING', () => {
     expect(source).toMatch(
       /self\.addEventListener\('message', \(event\) => \{\s*if \(event\.data\?\.type === 'SKIP_WAITING'\) void self\.skipWaiting\(\)/,