fix(economy): handle db_error in commands, dedupe cooldowns, single leaderboard scan

Three robustness/perf fixes from the review:

1. db_error UX: economy core returns {"ok": False, "reason": "db_error"} on a
   PocketBase outage, but no handler expected it - deferred commands hung on
   "thinking..." and others showed a misleading "you're broke". Added a shared
   reply_db_error helper (commands/_replies.py) + S.ERR["db_error"], and wired a
   db_error branch into every handler that can receive it (daily/work/beg/crime/
   rob/give/buy/roulette/slots/blackjack/heist/fish/prestige/vanity/consumables/
   request-funding). Also fixed a latent KeyError in vs-bot RPS that read
   res["balance"] without checking res["ok"].

2. Deduped the item->cooldown mapping that was copied in do_daily/do_work/do_beg,
   do_fish_start, _maybe_remind and _restore_reminders. Single source of truth:
   store.ITEM_COOLDOWNS + effective_cooldown(cmd, items).

3. /leaderboard did six full-collection scans (one per tab). Added
   get_all_leaderboards() which scans once and builds all six views in memory.

Tests: effective_cooldown cases, and get_all_leaderboards matches the individual
queries + scans the collection exactly once.

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

commands/_replies.py

@@ -0,0 +1,25 @@
+"""Shared reply helpers for command handlers."""
+
+from __future__ import annotations
+
+import discord
+
+import strings as S
+
+
+async def reply_db_error(interaction: discord.Interaction) -> None:
+    """Tell the user the database is unavailable.
+
+    Economy core functions return {"ok": False, "reason": "db_error"} on a
+    PocketBase outage. Without this, handlers either fall through silently (a
+    deferred interaction hangs on "thinking...") or show a misleading "you're
+    broke" message. Works whether or not the interaction was already deferred.
+    """
+    msg = S.ERR["db_error"]
+    try:
+        if interaction.response.is_done():
+            await interaction.followup.send(msg, ephemeral=True)
+        else:
+            await interaction.response.send_message(msg, ephemeral=True)
+    except discord.HTTPException:
+        pass