feat(code): cartes liées au code — branches, PRs, commits (issue #1)

app/code_links.py: appariement pur (#n dans titres/corps/messages,
numéro en jeton de branche). Client: list_branches/list_pulls/
list_commits. Badge sur les cartes (board + fragments live),
section Code lié du panneau détail, /api/issues/{o}/{r}/{n}/code.

app/templates/_card.html

@@ -19,6 +19,9 @@
                             {% endfor %}
                         </div>
                         {% endif %}
+                        {% if issue._code %}
+                        <div class="card-code">⑂{% if issue._code.branches %} 🌿 {{ issue._code.branches }}{% endif %}{% if issue._code.commits %} · {{ issue._code.commits }} commit{{ 's' if issue._code.commits > 1 }}{% endif %}{% if issue._code.pr %} · PR #{{ issue._code.pr.number }} {{ issue._code.pr.label }}{% endif %}</div>
+                        {% endif %}
                         <div class="card-meta">
                             {% if issue.assignee %}
                             <img src="{{ issue.assignee.avatar_url }}" class="avatar" alt="{{ issue.assignee.login }}">

app/templates/board.html

@@ -27,6 +27,7 @@
             <a href="/capture" class="nav-pill">⚡ Capture</a>
             <a href="/digest" class="nav-pill">🧠 Digest</a>
             <a href="/forecast" class="nav-pill">🔮 Prévisions</a>
+            <a href="/rules" class="nav-pill">⚙️ Règles</a>
             <a href="/wall" class="nav-pill">🖥️ Wallboard</a>
             <button type="button" class="nav-pill palette-trigger" title="Palette de commandes (Ctrl+K)">⌨️ Ctrl K</button>
             {% if repo_info.html_url %}
@@ -164,6 +165,7 @@
             <span class="notes-hint">Étiquettes de l'issue — cliquez pour ajouter / retirer :</span>
             <div id="detail-label-toggles" class="label-toggles"></div>
         </div>
+        <div id="detail-code" class="detail-code"></div>
         <div id="detail-body" class="detail-body"></div>
         <h3 class="detail-comments-title">💬 Commentaires</h3>
         <div id="detail-comments"></div>