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

README.md

@@ -347,6 +347,7 @@ The **ECONOMY** role is granted on your first EXP award (i.e. first successful e
 | `/vanity` | Status shop — buy and equip cosmetic badges/titles (shown on `/profile`). Coins are **burned**, not recirculated. No gameplay effect. |
 | `/reminders` | Toggle per-command DM notifications. Bot DMs you the moment each cooldown expires. |
 | `/quests` | Personal daily (3) and weekly (2) quests with progress bars and a claim button. |
+| `/achievements` | Milestone badges over your lifetime stats (work/wealth/gambling/crime/fishing/streaks/prestige). Each unlocks once and pays a one-time coin reward; opening the command claims any newly earned. |
 | `/fish` | Interactive fishing minigame. Cast, wait for bite, pull, then keep or sell. 2min cooldown (90s with Ussipurk). |
 | `/fishbook` | View your fish collection - all caught species, rarity, count, and current inventory amounts. |
 | `/fishsell` | Sell all fish currently in your inventory at once. |