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/forex_store.go

@@ -0,0 +1,140 @@
+package plugin
+
+import (
+	"gogobee/internal/db"
+)
+
+// ── Rate Storage ────────────────────────────────────────────────────────────
+
+func fxSaveRate(currency, date string, rate float64) {
+	db.Exec("forex: save rate",
+		`INSERT OR IGNORE INTO forex_rates (currency, date, rate) VALUES (?, ?, ?)`,
+		currency, date, rate)
+}
+
+type fxRateRecord struct {
+	Date string
+	Rate float64
+}
+
+// fxGetRates returns rates for a currency in the given date range, ordered by date.
+// Uses ORDER BY date DESC LIMIT n when limit > 0 (for "last N trading days").
+func fxGetRatesByLimit(currency string, limit int) ([]fxRateRecord, error) {
+	d := db.Get()
+	rows, err := d.Query(
+		`SELECT date, rate FROM forex_rates WHERE currency = ? ORDER BY date DESC LIMIT ?`,
+		currency, limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var records []fxRateRecord
+	for rows.Next() {
+		var r fxRateRecord
+		if err := rows.Scan(&r.Date, &r.Rate); err != nil {
+			continue
+		}
+		records = append(records, r)
+	}
+
+	// Reverse to chronological order (oldest first)
+	for i, j := 0, len(records)-1; i < j; i, j = i+1, j-1 {
+		records[i], records[j] = records[j], records[i]
+	}
+	return records, nil
+}
+
+// fxLatestRate returns the most recent stored rate for a currency.
+func fxLatestRate(currency string) (float64, bool) {
+	d := db.Get()
+	var rate float64
+	err := d.QueryRow(
+		`SELECT rate FROM forex_rates WHERE currency = ? ORDER BY date DESC LIMIT 1`,
+		currency).Scan(&rate)
+	if err != nil {
+		return 0, false
+	}
+	return rate, true
+}
+
+// ── Alert Storage ───────────────────────────────────────────────────────────
+
+type fxAlertRecord struct {
+	UserID    string
+	Currency  string
+	Threshold float64
+	FiredAt   int64
+}
+
+func fxSaveAlert(userID, currency string, threshold float64) error {
+	d := db.Get()
+	_, err := d.Exec(
+		`INSERT OR REPLACE INTO forex_alerts (user_id, currency, threshold, fired_at)
+		 VALUES (?, ?, ?, 0)`,
+		userID, currency, threshold)
+	return err
+}
+
+func fxAlertsForUser(userID string) ([]fxAlertRecord, error) {
+	d := db.Get()
+	rows, err := d.Query(
+		`SELECT user_id, currency, threshold, fired_at
+		 FROM forex_alerts WHERE user_id = ? ORDER BY currency, threshold`,
+		userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var alerts []fxAlertRecord
+	for rows.Next() {
+		var a fxAlertRecord
+		if err := rows.Scan(&a.UserID, &a.Currency, &a.Threshold, &a.FiredAt); err != nil {
+			continue
+		}
+		alerts = append(alerts, a)
+	}
+	return alerts, nil
+}
+
+func fxAllAlerts() ([]fxAlertRecord, error) {
+	d := db.Get()
+	rows, err := d.Query(
+		`SELECT user_id, currency, threshold, fired_at FROM forex_alerts`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var alerts []fxAlertRecord
+	for rows.Next() {
+		var a fxAlertRecord
+		if err := rows.Scan(&a.UserID, &a.Currency, &a.Threshold, &a.FiredAt); err != nil {
+			continue
+		}
+		alerts = append(alerts, a)
+	}
+	return alerts, nil
+}
+
+func fxDeleteAlert(userID, currency string, threshold float64) error {
+	d := db.Get()
+	_, err := d.Exec(
+		`DELETE FROM forex_alerts WHERE user_id = ? AND currency = ? AND threshold = ?`,
+		userID, currency, threshold)
+	return err
+}
+
+func fxMarkAlertFired(a fxAlertRecord) {
+	db.Exec("forex: mark alert fired",
+		`UPDATE forex_alerts SET fired_at = unixepoch() WHERE user_id = ? AND currency = ? AND threshold = ?`,
+		a.UserID, a.Currency, a.Threshold)
+}
+
+// fxResetExpiredAlerts clears fired_at for alerts that fired more than 24 hours ago,
+// allowing them to re-fire if the threshold is still met.
+func fxResetExpiredAlerts() {
+	db.Exec("forex: reset expired alerts",
+		`UPDATE forex_alerts SET fired_at = 0 WHERE fired_at > 0 AND fired_at < unixepoch() - 86400`)
+}