📝 Add docstrings to feat/go-rewrite

Docstrings generation was requested by @blakeridgway.

* https://github.com/RideAware/admin-panel/pull/1#issuecomment-3528008426

The following files were modified:

* `cmd/admin-panel/main.go`
* `internal/config/config.go`
* `internal/database/database.go`
* `internal/email/email.go`
* `internal/handlers/auth.go`
* `internal/handlers/newsletter.go`
* `internal/handlers/subscribers.go`
* `internal/middleware/auth.go`

internal/handlers/newsletter.go

@@ -8,10 +8,15 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
+// SendUpdateGet renders the update form page using the "send_update.html" template and responds with HTTP 200 OK.
 func SendUpdateGet(c *gin.Context) {
 	c.HTML(http.StatusOK, "send_update.html", gin.H{})
 }
 
+// SendUpdatePost handles POST requests to submit a newsletter update.
+// It reads "subject" and "body" from the form, calls email.SendUpdate(subject, body),
+// and renders the "send_update.html" template with gin.H{"error": message} when sending fails
+// or gin.H{"success": message} when sending succeeds, returning HTTP 200 in both cases.
 func SendUpdatePost(c *gin.Context) {
 	subject := c.PostForm("subject")
 	body := c.PostForm("body")