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

core/economy/leaderboards.py

@@ -80,3 +80,32 @@ async def get_leaderboard_fish(top_n: int | None = 10) -> list[tuple[str, int]]:
         reverse=True,
     )
     return result if top_n is None else result[:top_n]
+
+
+async def get_all_leaderboards() -> dict[str, list[tuple]]:
+    """Build every leaderboard view from a SINGLE collection scan.
+
+    /leaderboard shows six tabs; calling each get_leaderboard_* separately would
+    read the whole collection six times. This reads once and sorts in memory,
+    returning the same tuple shapes the individual functions produce (unbounded -
+    the command paginates)."""
+    records = await pb_client.list_all_records()
+    users = [r for r in records if r.get("user_id")]
+
+    def desc(keyfn) -> list[dict]:
+        return sorted(users, key=keyfn, reverse=True)
+
+    return {
+        "coins":    [(r["user_id"], r.get("balance", 0))
+                     for r in desc(lambda r: r.get("balance", 0))],
+        "exp":      [(r["user_id"], r.get("exp", 0), get_level(r.get("exp", 0)))
+                     for r in desc(lambda r: r.get("exp", 0))],
+        "season":   [(r["user_id"], r.get("season_total_exp", 0), r.get("prestige_level", 0))
+                     for r in desc(lambda r: r.get("season_total_exp", 0))],
+        "prestige": [(r["user_id"], r.get("prestige_level", 0), r.get("prestige_points", 0))
+                     for r in desc(lambda r: (r.get("prestige_level", 0), r.get("prestige_points", 0)))],
+        "wagered":  [(r["user_id"], r.get("total_wagered", 0))
+                     for r in desc(lambda r: r.get("total_wagered", 0))],
+        "fish":     [(r["user_id"], r.get("total_fish_caught", 0))
+                     for r in desc(lambda r: r.get("total_fish_caught", 0))],
+    }