Full codebase audit: 21 security/robustness fixes, 328 tests across 4 packages

Security & economy:
- Credit()/Debit() reject non-positive amounts (closes infinite-money exploit)
- Lottery ticket purchase uses in-transaction count check (closes TOCTOU race)
- Arena bail channel ownership prevents double-close panic
- Entry.ID validated before exec.Command in fetch-esteemed
- Internal errors no longer leaked to users (forex, esteemed)

Robustness:
- safeGo() panic recovery added to 17 goroutine launch sites across 14 plugins
- db.Close() added and called on shutdown
- Miniflux mutex pattern fixed (snapshot-under-lock)
- Silently ignored DB/JSON errors now logged (lottery_db)

Performance:
- Added indexes: idx_arena_runs_user(user_id, status), idx_euro_bal_user(user_id)

UX:
- Empty !buy args shows usage instead of "No item matching ''"
- "Failed to load character" now suggests !adventure

Test coverage:
- internal/util/parser_test.go (19 tests: XP, levels, progress bar, commands, parsing)
- internal/crypto/crypto_test.go (12 tests: encrypt/decrypt, HMAC, ParseKey)
- internal/plugin/helpers_test.go (30 tests: formatNumber, calc, lottery, chat perks)
- internal/plugin/audit_fixes_test.go (25 tests: safeGo, bail channels, error leaks, overflow)
- internal/db/db_test.go (4 tests: Init, Close, schema indexes)

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

internal/plugin/llm_passive.go

@@ -159,14 +159,14 @@ func (p *LLMPassivePlugin) OnMessage(ctx MessageContext) error {
 
 	// Check for fancy words on every message (independent of LLM sampling)
 	if p.dict != nil {
-		go func() {
+		safeGo("llm-fancy-word", func() {
 			if p.hasFancyWord(ctx.Body) {
 				_ = p.SendReact(ctx.RoomID, ctx.EventID, "\U0001f393") // 🎓 graduation cap
 				db.Exec("llm: track fancy word",
 					`UPDATE user_stats SET fancy_words = fancy_words + 1 WHERE user_id = ?`,
 					string(ctx.Sender))
 			}
-		}()
+		})
 	}
 
 	// Pre-filter: only classify messages that match certain criteria