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/commands.py

@@ -76,6 +76,7 @@ CMD: dict[str, str] = {
     "consumables":    "Sirvi ja osta turgutusi (korduvostetavad boostid)",
     "vanity":         "Staatusepood - osta ja kanna kosmeetilisi tiitleid",
     "lootbox":        "Ava õnnekast - juhuslik auhind müntide või boonuse näol",
+    "achievements":   "Vaata oma saavutusi ja teeni märkide eest ühekordseid preemiaid",
     "bank":           "Vaata oma panka - röövikindel hoius",
     "deposit":        "Pane münte panka (röövikindel, aga ei teeni intressi)",
     "withdraw":       "Võta münte pangast rahakotti",
@@ -159,6 +160,7 @@ HELP_CATEGORIES: dict[str, dict] = {
             ("/deposit <amount>", "Pane münte panka (röövikindel hoius, ei teeni intressi)."),
             ("/withdraw <amount>", "Võta münte pangast rahakotti."),
             ("/quests", "Vaata oma päeva- ja nädalaülesandeid ning nõua auhinnad (uueneb iga päev/nädal)."),
+            ("/achievements", "Vaata oma saavutusi. Iga lukust lahti saanud märk annab ühekordse müntipreemia."),
             ("/leaderboard", "TipiBOTi edetabel - kes on kõige rikkam?"),
             ("/shop", "Sirvi TipiBOTi poodi"),
             ("/buy <item>", "Osta ese TipiBOTi poodist"),