Add CAD currency, forex cross-pair support, and adventure timer fixes

Forex: add CAD to tracked currencies, add cross-pair syntax (EUR/USD,
EUR|JPY, etc.) for both !fx rate and !fx report with full historical
analysis computed from stored USD-base rates.

Adventure: fix midnight reset silently failing due to SQLite busy
contention with the reminder fire loop — propagate errors so the job
isn't marked complete on failure, add retry with backoff, and add
startup catch-up for missed resets and expired death timers.

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

internal/plugin/forex_analysis_test.go

@@ -0,0 +1,43 @@
+package plugin
+
+import (
+	"math/rand/v2"
+	"testing"
+)
+
+func BenchmarkComputeSignalFromRates(b *testing.B) {
+	// Simulate 260 trading days of rates around 150 (JPY-like)
+	rates := make([]float64, 261)
+	for i := range rates {
+		rates[i] = 145 + rand.Float64()*10
+	}
+	currentRate := rates[len(rates)-1]
+
+	b.ResetTimer()
+	for b.Loop() {
+		fxComputeSignalFromRates(rates, currentRate)
+	}
+}
+
+func BenchmarkComputeSignalFromRates_CrossPairSize(b *testing.B) {
+	// Simulate cross-pair: 260 days of EUR/JPY-like rates
+	baseRates := make([]float64, 260)
+	quoteRates := make([]float64, 260)
+	for i := range baseRates {
+		baseRates[i] = 0.90 + rand.Float64()*0.10  // EUR/USD ~0.90-1.00
+		quoteRates[i] = 145 + rand.Float64()*10     // JPY/USD ~145-155
+	}
+
+	// Compute cross-rates (simulating the join)
+	crossRates := make([]float64, len(baseRates)+1)
+	for i := range baseRates {
+		crossRates[i] = quoteRates[i] / baseRates[i]
+	}
+	crossRates[len(baseRates)] = quoteRates[len(quoteRates)-1] / baseRates[len(baseRates)-1]
+	currentRate := crossRates[len(crossRates)-1]
+
+	b.ResetTimer()
+	for b.Loop() {
+		fxComputeSignalFromRates(crossRates, currentRate)
+	}
+}