Let rules carry a note

A glob like *4412* says nothing about why it exists or who it catches, and
six months later neither does memory. Rules get an optional note: free text
that never takes part in matching, written as a TOML key rather than a
comment so it survives a round trip and can be shown back.

The rule builder grows a fourth field for it and the rules screen a last
column. Four fields spaced out are taller than a short window has room for,
so the form now drops its blank lines and then the hints on unfocused fields
before anything would run off the bottom.

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

internal/config/config_test.go

@@ -196,6 +196,63 @@ func TestAppendRuleQuotesValues(t *testing.T) {
 	}
 }
 
+// A note is documentation carried with the rule. It is a key rather than a
+// comment precisely so it survives the round trip.
+func TestAppendRuleWithNote(t *testing.T) {
+	root := t.TempDir()
+	note := `the "corner shop" — 4412 is the branch code`
+	if err := AppendRule(root, Rule{Match: "*4412*", Tag: "groceries", Note: note}); err != nil {
+		t.Fatal(err)
+	}
+	loaded, err := LoadRules(root)
+	if err != nil {
+		t.Fatalf("the note broke the file: %v", err)
+	}
+	if loaded.Rule[0].Note != note {
+		t.Errorf("note = %q, want %q", loaded.Rule[0].Note, note)
+	}
+	// A note alone is not a rule; the usual validation still applies.
+	if err := AppendRule(root, Rule{Note: "just a thought"}); err == nil {
+		t.Error("expected a rule with only a note to be rejected")
+	}
+}
+
+// Deleting a rule takes its note with it and leaves everyone else's alone.
+func TestDeleteRuleTakesItsNote(t *testing.T) {
+	root := t.TempDir()
+	path := filepath.Join(root, RulesFile)
+	original := `[[rule]]
+match = "*LIDL*"
+tag   = "groceries"
+note  = "the weekly shop"
+
+[[rule]]
+match = "*ZARA*"
+tag   = "clothes"
+note  = "keep: for the January review"
+`
+	if err := os.WriteFile(path, []byte(original), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := DeleteRules(root, []int{0}); err != nil {
+		t.Fatal(err)
+	}
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(raw), "weekly shop") {
+		t.Errorf("rules.toml = %q, want the deleted rule's note gone with it", raw)
+	}
+	loaded, err := LoadRules(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(loaded.Rule) != 1 || loaded.Rule[0].Note != "keep: for the January review" {
+		t.Errorf("rules = %+v, want the surviving rule to keep its note", loaded.Rule)
+	}
+}
+
 const rulesWithComments = `# Rules for my accounts.
 # Order matters: the first match wins.