Add polished answer notifications (#1)

Sends a branded Resend email when a question receives its first answer, records accepted and failed sends, and adds collapsed answer editing with cancel behavior.

Co-authored-by: codegirl-007 <s.raide@gmail.com>

templates/partials/_answer.html

@@ -5,6 +5,22 @@
     <h2>Answer</h2>
     <p class="byline">{{.Answer.AuthorName}} · 22 years, Bay Area</p>
     <p class="answer-body">{{.Answer.Body}}</p>
+    {{if isAdmin .User}}
+      <details class="answer-editor">
+        <summary>Edit answer</summary>
+        <form class="answer-form" method="post" action="/questions/{{.Answer.QuestionID}}/answer"
+          hx-post="/questions/{{.Answer.QuestionID}}/answer" hx-target="#answer-block" hx-swap="outerHTML">
+          <input type="hidden" name="_csrf" value="{{.CSRF}}">
+          <label for="answer-body">Edit answer</label>
+          <textarea id="answer-body" name="body" rows="8" required maxlength="12000">{{.Answer.Body}}</textarea>
+          <div class="answer-form-actions">
+            <button type="submit" class="btn btn-primary">Save answer</button>
+            <button type="reset" class="btn btn-ghost"
+              onclick="this.closest('details').removeAttribute('open')">Cancel</button>
+          </div>
+        </form>
+      </details>
+    {{end}}
   {{else}}
     <p class="waiting">No answer yet. Check back after the hunt.</p>
   {{end}}