Fix the mode-choice redundancy: standardized names, deep links, compact switch

Terminology (lib/i18n-dict.ts)
- One name per mode everywhere: "Study Deck" / "Studijní balíček" and
  "Homework Solver" / "Řešitel úkolů". The library empty-state cards and the
  /create switcher now read the same, so the choice no longer changes name
  between screens.

Deep links
- Library quick actions carry the mode: /create?mode=deck and
  /homework?mode=homework.
- Both pages canonicalize: /create?mode=homework redirects to the homework
  flow and /homework?mode=deck redirects to /create, so a mode link always
  opens that mode directly.

/create
- The two bulky square cards (106px tall, wrapping/clipping "Study Deck &
  Qu…" on phones) are replaced by a compact segmented control (52px) placed
  directly above "1. Add your notes": ice pill, snowflake/sparkles icons,
  44px segments and one-line labels at 360px. The pill slides to the chosen
  segment and the route follows ~190ms later, so toggling reads as one smooth
  transition (immediate under prefers-reduced-motion).

Service worker: freezmo-v9.

Verified: mode-switch suite 26/26 (deep links, cross-mode redirects, 52px
control, 44px segments, no clipping/wrapping at 360px, "1. Add your notes" at
y=394 of 740 with the upload controls above the fold, pill slide, axe contrast,
en+cs, phone+desktop), mobile 49/49, i18n 27/27, desktop regression 73/73.
Lint + build clean.

lib/i18n-dict.ts

@@ -224,9 +224,9 @@ const en: Record<string, string> = {
   "homework.history.deleteConfirm": "Delete this result?",
 
   /* quick actions (library empty state + /create switcher) ----------- */
-  "emptyStateCreateDeck": "Create interactive test",
-  "emptyStateHomework": "Help me with my homework",
-  "actionStudyDeck": "Study Deck & Quizzes",
+  "emptyStateCreateDeck": "Study Deck",
+  "emptyStateHomework": "Homework Solver",
+  "actionStudyDeck": "Study Deck",
   "actionHomework": "Homework Solver",
 
   /* library --------------------------------------------------------- */
@@ -808,9 +808,9 @@ const cs: Record<string, string> = {
   "homework.history.deleteConfirm": "Smazat tento výsledek?",
 
   /* quick actions (library empty state + /create switcher) ----------- */
-  "emptyStateCreateDeck": "Vytvořit interaktivní test",
-  "emptyStateHomework": "Pomoct s úkolem",
-  "actionStudyDeck": "Studijní balíček a testy",
+  "emptyStateCreateDeck": "Studijní balíček",
+  "emptyStateHomework": "Řešitel úkolů",
+  "actionStudyDeck": "Studijní balíček",
   "actionHomework": "Řešitel úkolů",
 
   /* library --------------------------------------------------------- */