fix(ux): apply UX quick wins (#54)

Get started links to registration and says an admin approves accounts.
Back navigation restores the library scroll; search no longer fills history.
Steam and PSN unlink ask first. Any close marks news as seen.
Confetti plays only when the level rises on the page.
Count-ups respect reduced motion. Html lang follows the UI language.
Add a 404 page, translated role and dialog close label.

public/i18n/en.json

@@ -132,6 +132,10 @@
       "VERIFY": "Verify with Steam",
       "CHANGE": "Link another Steam account",
       "UNLINK": "Unlink",
+      "UNLINK_TITLE": "Unlink Steam account?",
+      "UNLINK_EXPLAIN": "The Steam sync stops. Your games stay in your library. To sync again, link the account again.",
+      "UNLINK_CONFIRM": "Yes, unlink",
+      "UNLINK_ERROR": "Could not unlink the Steam account.",
       "VERIFIED": "Verified",
       "NOT_VERIFIED": "Not verified",
       "NONE": "No Steam account linked yet. You sign in on Steam, and Steam tells us your Steam ID; we never see your Steam password.",
@@ -159,6 +163,9 @@
       "SYNC_HINT": "Every sync brings in newly played titles. Clear matches are added; unclear ones wait in the import review.",
       "REVIEW": "Review waiting titles",
       "UNLINK": "Unlink",
+      "UNLINK_TITLE": "Unlink PlayStation account?",
+      "UNLINK_EXPLAIN": "The PlayStation sync stops. Imported games stay in your library. To sync again, paste a new NPSSO code.",
+      "UNLINK_CONFIRM": "Yes, unlink",
       "UNLINKED": "PlayStation account unlinked. Imported games stay in your library.",
       "INVALID": "PlayStation did not accept the code. It may have expired: sign in again and copy a new one.",
       "UNAVAILABLE": "PlayStation did not answer. Please try again later.",
@@ -367,6 +374,7 @@
     "WELCOME": "Control your game backlog",
     "DESCRIPTION": "Organize your pile of shame. Track, manage, and conquer your gaming backlog like never before.",
     "GET_STARTED": "Get Started",
+    "APPROVAL_HINT": "An admin approves every new account before the first login.",
     "LOGIN": "Log in",
     "LOGOUT": "Log out"
   },
@@ -674,6 +682,13 @@
       "GAMES_other": "{{count}} games"
     }
   },
+  "DIALOG": {
+    "CANCEL": "Cancel",
+    "CLOSE": "Close"
+  },
+  "NOT_FOUND": {
+    "TITLE": "Page not found"
+  },
   "ROLES": {
     "USER": "User",
     "AUDITOR": "Auditor",