Add “Make my homework”, and finish the mobile polish pass

Homework (/homework — entry points in the drawer and on the create screen)

- Assignment intake reuses the study pipeline: pasted text, photos
  (camera/picker, compressed in the browser) and documents (PDF/DOCX/PPTX/
  ODT/text) through lib/image + lib/documents, the same vision step and the
  same language guard. Raw files never leave the device — only text and JPEG
  data URLs reach the server.
- Two large choice cards: “Just make it” returns the finished homework
  (answer only, plain text, copy + make it again); “Explain how to make this
  homework” builds an interactive guide.
- The guide is one step per screen in the study-feed snap layout:
  explanation, three progressive hints (nudge -> hint -> the answer) and an
  optional checkpoint rendered by the existing activity components (graded
  through /api/grade). The last screen assembles the solution from the step
  answers, with a copy button. Checkpoints carry xp 0 so the guide stays free
  of XP/streak chrome.
- Results live in freezmo.homework.v1 with a small history (open/delete);
  “Make it again” re-runs from the stored assignment text (the vision
  transcription when photos were used) — no original files are stored.
- The answer and the guide are written in the assignment's language, never
  translated into the UI language.

Server

- POST /api/homework: NDJSON stage events like /api/generate, the same
  http-guard, auth checked before parsing, and its own RATE_LIMIT_HOMEWORK
  (documented in .env.example + the README table).
- New prompts in lib/prompts.ts and zod schemas in lib/schemas.ts with the
  same single repair retry; TEXT_MODEL for content, VISION_MODEL only for
  photos. New shared client pieces: useNotesIntake, lib/homework store,
  lib/clipboard, and a shared NDJSON reader in lib/client-api.

Also finishing the mobile polish pass from the previous request

- Phone ice scene: the top-left orb moved behind the glass header (it sat
  behind the page heading/subtitle). The settings sheet's scroll cue is now a
  bare chevron inside a content fade (mask) instead of a chip over the status
  banner, and the API key card's note/disclosure/actions are tightened.
- theme-color now follows the in-app theme (SSR metas still fall back to the
  OS preference); apple-mobile-web-app-status-bar-style stays “default”
  because iOS fixes the status-bar text colour at launch.

Verified: 78/78 homework checks (text/photo/PDF, both modes, EN+CS, dark+light,
360/390px, copy, history persistence, storage privacy, API language, axe), plus
the existing suites re-run (mobile 47/47, pixel contrast 0 below AA, i18n 27/27,
desktop regression 72/72). Lint + build clean; service worker freezmo-v6.

app/globals.css

@@ -338,7 +338,9 @@ body {
     --ice-blob-opacity: 0.2;
     --ice-orb-opacity: 0.42;
   }
-  .ice-orb-1 { width: 96px; height: 96px; top: 8%; left: -26px; }
+  /* Tucked up behind the glass header: at top 8% it sat right behind the page
+     heading and subtitle. */
+  .ice-orb-1 { width: 88px; height: 88px; top: -30px; left: -38px; }
   .ice-orb-2 { width: 72px; height: 72px; left: -32px; }
   /* Was sitting right behind the bottom-nav labels. */
   .ice-orb-3 { width: 116px; height: 116px; bottom: 15vh; right: -46px; }
@@ -698,10 +700,15 @@ body {
 }
 
 /* Settings sheet: contained momentum scrolling; the safe-area padding comes
-   from the pb-safe utility plus a trailing spacer. */
+   from the pb-safe utility plus a trailing spacer. The mask fades the last
+   36px of *content* (not a coloured overlay, so it blends with the glass in
+   both themes) — that is the scroll cue; the trailing spacer keeps real
+   content out of the faded strip once you reach the bottom. */
 .sheet-scroll {
   overscroll-behavior: contain;
   -webkit-overflow-scrolling: touch;
+  -webkit-mask-image: linear-gradient(to bottom, #000 calc(100% - 36px), transparent);
+  mask-image: linear-gradient(to bottom, #000 calc(100% - 36px), transparent);
 }
 }