docs(comments): add some comments

this is the subject of the commit

api/handlers/cards.go

@@ -180,7 +180,7 @@ func (h *CardHandler) CollectCard(w http.ResponseWriter, r *http.Request) {
 
 // SaveCardRequest holds the raw card fields submitted by the TUI.
 // Tokenization happens server-side so the Stripe secret key never
-// touches the SSH client or TUI layer..
+// touches the SSH client or TUI layer.
 type SaveCardRequest struct {
 	Token string `json:"token"`
 }

pkg/notify/slack.go

@@ -1,3 +1,4 @@
+// Package notify provides a simple interface to send notifications to Slack.
 package notify
 
 import (
@@ -14,8 +15,10 @@ import (
 	"terminalShop/pkg/models"
 )
 
+// slack client
 var slackClient = &http.Client{Timeout: 5 * time.Second}
 
+// dollars converts cents to dollars
 func dollars(cents int) string {
 	return fmt.Sprintf("$%.2f", float64(cents)/100)
 }