Native-feel pass: PWA integration, system back, offline, haptics, undo

Mobile only (<=639px / coarse pointers); desktop keeps its behaviour.

System integration
- Manifest: id, display_override, monochrome icon, Make my homework
  shortcut and a share target (text/URL via GET, files via POST).
  iOS startup images for the common iPhone sizes. Pinch-zoom is allowed
  again (double-tap zoom is disabled via touch-action instead).
- Share target: /share chooser with New deck / Make my homework; POSTed
  files wait in a 10-minute in-memory store, reach the wizard through
  sessionStorage and never touch disk.
- Web Share: Share rows for decks (JSON file where supported) and the
  homework result, with a clipboard fallback and a toast.
- Offline: a quiet pill appears and Freeze / mode cards are disabled
  with a clear reason; input is never lost (error cards keep Retry).
- State: wizard drafts (text, options, photos up to a size budget)
  survive reloads and OS kills and are cleared on success; re-tapping
  the active tab scrolls to the top; the deck page shows a skeleton
  instead of a spinner.

Navigation and gestures
- System Back closes the topmost layer first: a small history-entry
  stack (lib/use-back-close.ts) covers the drawer, Settings sheet,
  install sheet, deck actions panel and one wizard step; navigations
  are never rewound and stale entries are skipped.
- Destructive-but-reversible actions use Undo toasts: deleting a deck
  (no confirm) and removing a file in the wizard. Irreversible ones
  keep their confirm.

Input and feedback
- Every phone input got inputmode / enterkeyhint / autocomplete /
  autocapitalize / spellcheck; Enter on the last field advances the
  wizard; a clipboard-paste button appears where the API exists.
- Haptics behind a Settings toggle (on by default): tab switches,
  toggles, correct/wrong, completion; Vibration API + the iOS hidden
  switch tick, throttled and silent everywhere else.
- Wake lock during the study feed and homework guide, released on
  leave and re-acquired when the tab returns.

Verified: new native suite 35/35 (manifest/head/viewport, offline,
share target GET + POST, back-gesture layers, undo, share fallback,
tab re-tap, haptics persistence, draft restore), regression 74/74,
mobile 52/52, wizard 80/80, declutter 116/116, animation 8/8,
i18n 25/25. Lint + build clean. SW freezmo-v23.

Needs a real device (documented in the README): iOS haptic tick,
system share sheet entry, wake-lock grant, iPhone startup images,
iOS edge-swipe back, install prompts. Pull-to-refresh and the app
badge were skipped on purpose.

app/manifest.ts

@@ -6,6 +6,7 @@ import type { MetadataRoute } from "next";
  */
 export default function manifest(): MetadataRoute.Manifest {
   return {
+    id: "/",
     name: "Freezmo — notes to study feed",
     short_name: "Freezmo",
     description:
@@ -13,6 +14,7 @@ export default function manifest(): MetadataRoute.Manifest {
     start_url: "/",
     scope: "/",
     display: "standalone",
+    display_override: ["standalone", "minimal-ui"],
     orientation: "portrait",
     background_color: "#0e1424",
     theme_color: "#0e1424",
@@ -21,10 +23,39 @@ export default function manifest(): MetadataRoute.Manifest {
       { src: "/icons/icon-192.png", sizes: "192x192", type: "image/png", purpose: "any" },
       { src: "/icons/icon-512.png", sizes: "512x512", type: "image/png", purpose: "any" },
       { src: "/icons/maskable-512.png", sizes: "512x512", type: "image/png", purpose: "maskable" },
+      { src: "/icons/monochrome.svg", sizes: "any", type: "image/svg+xml", purpose: "monochrome" },
     ],
     shortcuts: [
       { name: "New deck", short_name: "New", url: "/create" },
+      { name: "Make my homework", short_name: "Homework", url: "/homework" },
       { name: "Library", short_name: "Library", url: "/" },
     ],
+    /* Share text and links from other apps (GET). Files are POSTed to the
+       same route and handed over through a short-lived in-memory store. */
+    share_target: {
+      action: "/share-target",
+      method: "POST",
+      enctype: "multipart/form-data",
+      params: {
+        title: "title",
+        text: "text",
+        url: "url",
+        files: [
+          {
+            name: "files",
+            accept: [
+              "image/*",
+              "application/pdf",
+              "text/*",
+              "application/msword",
+              "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+              "application/vnd.openxmlformats-officedocument.presentationml.presentation",
+              "application/vnd.oasis.opendocument.text",
+              "application/vnd.oasis.opendocument.presentation",
+            ],
+          },
+        ],
+      },
+    },
   };
 }