Mobile declutter pass: step flows, compact cards, simplified settings

Phones only (<=639px); desktop markup is untouched.

- New deck is a 3-step flow: progress (1/3 + bar) and a fixed Back/Next
  bar above the tab bar. Step 1 = Add photos or files / Camera / Paste
  text instead (no drop zone or paste copy on touch), step 2 = folder,
  difficulty and count with defaults plus one collapsed focus/notes row,
  step 3 = one summary line (photos/docs/text · difficulty · count ·
  folder) with Freeze. Going Back keeps every input; step transitions
  respect prefers-reduced-motion.
- Make my homework is a 2-step flow sharing the same pattern; tapping a
  mode card starts it (no separate CTA on phones), with a short preview
  of the assignment on step 2. The hero is now 'Make my homework' /
  'Udělej mi úkol' everywhere ('Solve your homework' is gone) and the
  intro is one line.
- Library: stats line removed, folder row and 'Unorganized' heading
  hidden until folders exist (New folder lives in the drawer), Import is
  a small icon button beside the tabs. Deck and homework cards are
  compact on phones: title, one meta line (activities · difficulty ·
  best), a one-line description that expands on tap, the whole card
  tappable and a small Study/Open pill instead of the full-width button.
- Settings sheet on phones: no .env.local subtitle; Language stays first;
  one Connection card (status dot + 'Connected · 2 models ready', key
  field with the eye inside, Save only when edited, auto re-check on
  save, refresh icon instead of Test connection); privacy one-liner with
  a More expander (daemon tip inside); raw health rows behind one
  collapsed Details list; Remove key as a small danger button at the very
  bottom (same confirmation).
- Decorative orbs on phones moved further off the screen edges so they
  never glow under cards or primary buttons.
- Shared markup for folder/difficulty/count and mode cards keeps one
  source of state; new lib/use-phone.ts gates the layouts.

Verified: new declutter suite 116/116 (360 + 390, EN + CS, photo + PDF +
pasted text, Back keeps input, summaries, settings flow), regression
74/74, mobile 52/52, i18n 25/25. Lint + build clean. SW freezmo-v20.

lib/use-phone.ts

@@ -0,0 +1,22 @@
+"use client";
+
+import { useEffect, useState } from "react";
+
+/**
+ * True on phone-sized viewports (≤639px), false during SSR and on desktop.
+ * The mobile-only step flows switch on this; everything wider keeps the
+ * desktop layout untouched.
+ */
+export function useIsPhone(): boolean {
+  const [phone, setPhone] = useState(false);
+
+  useEffect(() => {
+    const query = window.matchMedia("(max-width: 639px)");
+    const sync = () => setPhone(query.matches);
+    sync();
+    query.addEventListener("change", sync);
+    return () => query.removeEventListener("change", sync);
+  }, []);
+
+  return phone;
+}