feat: add leaderboard router, gamification backfill, and shared content creation helpers

Introduce a new `/leaderboard` endpoint ranking top 50 members by total stars, wire it into the app router and documentation. Implement `_backfill_gamification()` in `database.py` to compute XP/levels for existing accounts from prior posts, comments, votes, and follows. Extract `is_owner()`, `create_content_item()`, and `detail_context()` into `content.py` to centralize content creation, reward awarding, mention notifications, and attachment linking. Update comment creation/deletion in `comments.py` to use `award_rewards()` with `XP_COMMENT` and the new `is_owner()` helper. Add shared template partials documentation for vote bars, star buttons, post headers, and topic selectors to `AGENTS.md`.

devplacepy/templates/gist_detail.html

@@ -1,4 +1,5 @@
 {% extends "base.html" %}
+{% from "_macros.html" import modal %}
 {% block extra_head %}
 <link rel="stylesheet" href="/static/css/gists.css">
 <link rel="stylesheet" href="/static/css/post.css">
@@ -45,10 +46,7 @@
         <div class="gist-detail-actions">
             <button type="button" class="gist-star-btn" data-share="/gists/{{ gist['slug'] or gist['uid'] }}">&#x1F517; Share</button>
             {% if user %}
-            <form method="POST" action="/votes/gist/{{ gist['uid'] }}" style="display:inline;">
-                <input type="hidden" name="value" value="1">
-                <button type="submit" class="gist-star-btn">&#x2606; <span class="vote-count-value" data-vote-count="{{ gist['uid'] }}">{{ star_count }}</span></button>
-            </form>
+            {% set _type = "gist" %}{% set _uid = gist['uid'] %}{% set _my_vote = my_vote %}{% set _count = star_count %}{% set _btn_class = "gist-star-btn" %}{% include "_star_vote.html" %}
             {% endif %}
             {% if is_owner %}
             <button class="gist-star-btn" data-modal="edit-gist-modal"><span class="icon">&#x270F;&#xFE0F;</span>Edit</button>
@@ -60,12 +58,7 @@
     </article>
 
     {% if is_owner %}
-    <div class="modal-overlay" id="edit-gist-modal">
-        <div class="card modal-card modal-card-wide">
-            <div class="modal-header">
-                <h3>Edit Gist</h3>
-                <button type="button" class="modal-close btn-ghost btn-icon modal-close-btn">&times;</button>
-            </div>
+    {% call modal('edit-gist-modal', 'Edit Gist', wide=true) %}
             <form method="POST" action="/gists/edit/{{ gist['slug'] or gist['uid'] }}">
                 <div class="auth-field auth-field-gap">
                     <label for="edit-gist-title">Title</label>
@@ -93,8 +86,7 @@
                     <button type="submit" class="btn btn-primary"><span class="icon">&#x1F4BE;</span>Save Changes</button>
                 </div>
             </form>
-        </div>
-    </div>
+    {% endcall %}
     {% endif %}
 
     {% with target_uid=gist['uid'], target_type="gist" %}