Add nested posts UI (#5)

## Summary
- Cut hunt, question, submission, voting, hiding, and profile flows over to unified posts
- Render nested replies with permission-aware inline Reply/Edit controls and edited markers
- Add post profile queries and the author index migration they depend on

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

templates/profile.html

@@ -43,12 +43,12 @@
 
   <section class="profile-questions" aria-labelledby="profile-q-heading">
     <h2 id="profile-q-heading">{{.QuestionsLabel}}</h2>
-    {{if .Questions}}
+    {{if .Posts}}
       <ul class="profile-q-list">
-        {{range .Questions}}
+        {{range .Posts}}
           <li>
             <a href="/questions/{{.ID}}">{{.Title}}</a>
-            <span class="meta">{{.HuntDate}}</span>
+            <span class="meta">{{.PostDate}}</span>
           </li>
         {{end}}
       </ul>