Add forex plugin, stability fixes, and async HTTP dispatch

- Add forex plugin (Frankfurter v2 API) with rate lookups, analysis,
  DM-based alerts, and daily cron poll. Backfills 1 year of history
  on startup for moving averages and buy signal scoring.

- Fix bot hang caused by SQLite lock contention in reminder polling:
  rows cursor was held open while writing to the same DB. Collect
  results first, close cursor, then process. Same fix in milkcarton.

- Add sync retry loop so the bot reconnects after network drops
  instead of silently exiting. StopSync() for clean Ctrl+C shutdown.

- Add panic recovery to all dispatch, syncer, and cron paths.

- Make all HTTP-calling plugin commands async (goroutines) so a slow
  or dead external API cannot block the message dispatch pipeline.
  Affects: lookup, stocks, forex, anime, movies, concerts, gaming,
  retro, wotd, urls, howami.

- Extract DisplayName to Base, add db.Exec helper, convert silent
  error discards across the codebase.

- Fix UNO mercy-kill bug (eliminated bot continues playing), adventure
  DM nag spam, stats column mismatch, per-call regex/replacer allocs.

- Update README: forex commands, Finance section, 47 plugins.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/plugin/adventure_activities.go

@@ -317,11 +317,14 @@ func advIsEligible(char *AdventureCharacter, equip map[EquipmentSlot]*AdvEquipme
 		return false, false
 	}
 
-	// Check minimum equipment tier
-	minTier := 99
-	for _, eq := range equip {
-		if eq.Tier < minTier {
-			minTier = eq.Tier
+	// Check minimum equipment tier — no equipment means tier 0
+	minTier := 0
+	if len(equip) > 0 {
+		minTier = 99
+		for _, eq := range equip {
+			if eq.Tier < minTier {
+				minTier = eq.Tier
+			}
 		}
 	}
 	if minTier < loc.MinEquipTier {