feat(economy): add /achievements milestone badges

15 one-time achievements over the lifetime stat counters (work/wealth/gambling/
crime/heists/fishing/streaks/prestige), each paying a modest one-time coin reward
when unlocked. Detection is lazy - opening /achievements claims any newly earned
(like quests roll on view) - so no per-command hook is needed, and rewards are a
bounded, one-time coin source.

- New achievements.py: ACHIEVEMENTS table, pure newly_earned/achievements_view,
  and locked do_check_achievements. New achievements_earned schema field.
- /achievements command (own view claims; viewing others is read-only) with
  progress bars, db_error handling, and an "unlocked" banner.

8 tests: threshold detection, one-time claim (no double pay), multi-unlock,
view progress capping.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013VbAVsrZuYesea99mPMmPT

strings/economy.py

@@ -20,6 +20,7 @@ __all__ = [
     'VANITY_UI',
     'LOOTBOX_UI',
     'BANK_UI',
+    'ACHIEVEMENTS_UI',
     'JAILED_UI',
     'SHOP_BTN',
     'DAILY_UI',
@@ -290,6 +291,17 @@ BANK_UI: dict[str, str] = {
     "nothing_bank":   "❌ Sul pole nii palju raha pangas.",
 }
 
+# ---------------------------------------------------------------------------
+# Achievements  (one-time milestone badges over lifetime stats)
+# ---------------------------------------------------------------------------
+ACHIEVEMENTS_UI: dict[str, str] = {
+    "title":         "🏅 Saavutused",
+    "desc":          "Iga lukust lahti saanud märk annab ühekordse müntipreemia.\nAvatud: **{earned}/{total}**",
+    "row_earned":    "✅ {emoji} **{name}**  ·  +{reward}",
+    "row_locked":    "🔒 {emoji} {name}  ·  {progress}/{goal}  ·  +{reward}",
+    "unlocked_note": "🎉 **Uued saavutused avatud:** {names}\n💰 Preemia: +{reward}",
+}
+
 JAILED_UI: dict[str, str] = {
     "title":      "🔒 Praegu vanglas",
     "empty":      "Kõik on vabad! Vanglas pole kedagi.",