Add a rules screen that finds and removes dead rules

Nothing showed whether a rule was still earning its place. The new screen, on
5, lists every rule in file order with the number of transactions it claims,
marking those that claim none.

The count comes from Engine.Usage, which counts by first match, so a rule
shadowed by an earlier one reports zero even though its glob matches. That is
the case worth catching: such a rule looks correct in isolation and can never
fire.

d removes the selected rule and p removes every unused one, each behind a y/n
confirmation since this rewrites a hand-maintained file. config.DeleteRules
edits rules.toml textually rather than re-serialising the parsed rules, so
comments and layout survive; a comment directly above a rule goes with it,
while one separated by a blank line is left as a heading. The result is
re-parsed before it replaces the file.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/rules/rules_test.go

@@ -139,6 +139,52 @@ func TestFirstMatchWins(t *testing.T) {
 	}
 }
 
+// A rule can be dead two ways: nothing matches it, or an earlier rule already
+// claimed everything it would have caught. Usage must report both as zero.
+func TestUsageCountsFirstMatchOnly(t *testing.T) {
+	engine := New(&config.Rules{Rule: []config.Rule{
+		{Match: "*LIDL*", Tag: "groceries"},        // claims both LIDL rows
+		{Match: "*LIDL SOFIA*", Tag: "shadowed"},   // fully shadowed by the above
+		{Match: "*NOTHING MATCHES ME*", Tag: "no"}, // matches nothing at all
+		{Match: "*PAYROLL*", Tag: "salary"},        // claims one row
+	}})
+
+	txns := []model.Transaction{
+		{AccountSlug: "checking", Description: "LIDL SOFIA 4412"},
+		{AccountSlug: "checking", Description: "LIDL VARNA 9911"},
+		{AccountSlug: "checking", Description: "ACME PAYROLL"},
+		{AccountSlug: "checking", Description: "UNMATCHED SHOP"},
+	}
+
+	usage := engine.Usage(txns)
+	want := []int{2, 0, 0, 1}
+	if len(usage) != len(want) {
+		t.Fatalf("usage has %d entries, want %d", len(usage), len(want))
+	}
+	for i := range want {
+		if usage[i] != want[i] {
+			t.Errorf("rule %d used by %d transactions, want %d", i+1, usage[i], want[i])
+		}
+	}
+}
+
+func TestMatchIndex(t *testing.T) {
+	engine := New(&config.Rules{Rule: []config.Rule{
+		{Match: "*LIDL EXPRESS*", Tag: "snacks"},
+		{Match: "*LIDL*", Tag: "groceries"},
+	}})
+
+	if got := engine.MatchIndex("checking", model.Transaction{Description: "LIDL EXPRESS 1"}); got != 0 {
+		t.Errorf("index = %d, want 0", got)
+	}
+	if got := engine.MatchIndex("checking", model.Transaction{Description: "LIDL 1"}); got != 1 {
+		t.Errorf("index = %d, want 1", got)
+	}
+	if got := engine.MatchIndex("checking", model.Transaction{Description: "OTHER"}); got != -1 {
+		t.Errorf("index = %d, want -1 for no match", got)
+	}
+}
+
 func TestAccountScopedRule(t *testing.T) {
 	engine := New(&config.Rules{Rule: []config.Rule{
 		{Match: "*TRANSFER*", Tag: "transfer", Transfer: true, Account: "savings"},