feat(economy): add /consumables shop of repeatable, expiring boosts

The economy had many coin faucets but almost no sinks: the /shop is
one-time ownership, and gambling/rob fines route to the house (which
players drain back via jackpots and heists), so they recirculate rather
than destroy coins. Result: steady inflation.

Add a consumables shop as a true recurring sink - buying destroys the
coins and grants a temporary boost, so there's always something to spend
on after gear is maxed:

  - Energiajook XL (500) - 1h of 2x earnings on /work, /beg, /crime
  - XP jook (500)        - 1h of 2x EXP
  - Kohv (300)           - instantly clears all cooldowns

Timed buffs live in a new active_buffs field ({kind: expiry_iso}), pruned
on read; rebuying extends the timer. Effects hook where they belong:
earn_mult in income.do_work/do_beg/do_crime, exp_buff_mult in
levels.award_exp; kohv is self-contained. New /consumables command browses
the menu (with active buffs) or buys a boost. Covered by 9 tests.

Note: active_buffs is a new PocketBase field - run
scripts/sync_pb_schema.py before deploying or buffs won't persist.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

strings/__init__.py

@@ -56,6 +56,8 @@ from .economy import (
     QUEST_DESCRIPTIONS,
     SHOP_UI,
     ITEM_DESCRIPTIONS,
+    CONSUMABLES_UI,
+    CONSUMABLE_DESCRIPTIONS,
     JAILED_UI,
     SHOP_BTN,
     DAILY_UI,
@@ -146,6 +148,8 @@ __all__ = [
     'QUEST_DESCRIPTIONS',
     'SHOP_UI',
     'ITEM_DESCRIPTIONS',
+    'CONSUMABLES_UI',
+    'CONSUMABLE_DESCRIPTIONS',
     'JAILED_UI',
     'SHOP_BTN',
     'DAILY_UI',