feat(web): add navigation menu bar for logged-in users

- Add horizontal nav menu with 7 items: Profile, Characters, Sessions,
  Mechanics, Leaderboard, Settings, Help
- Implement responsive hamburger menu for mobile (≤768px)
- Create pages blueprint with stub routes for new pages
- Add "Coming Soon" styled stub templates with icons
- Include active state highlighting for current page

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

public_web/templates/pages/sessions.html

@@ -0,0 +1,27 @@
+{% extends "base.html" %}
+
+{% block title %}Sessions - Code of Conquest{% endblock %}
+
+{% block content %}
+<div class="page-container">
+    <div class="coming-soon-card">
+        <h1 class="page-title">Game Sessions</h1>
+        <div class="coming-soon-icon">
+            <svg xmlns="http://www.w3.org/2000/svg" width="64" height="64" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
+                <path d="M14.5 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V7.5L14.5 2z"/>
+                <polyline points="14 2 14 8 20 8"/>
+                <line x1="16" y1="13" x2="8" y2="13"/>
+                <line x1="16" y1="17" x2="8" y2="17"/>
+                <line x1="10" y1="9" x2="8" y2="9"/>
+            </svg>
+        </div>
+        <p class="coming-soon-text">Coming Soon</p>
+        <p class="coming-soon-description">
+            View and manage your active game sessions. Resume adventures where you left off.
+        </p>
+        <a href="{{ url_for('character_views.list_characters') }}" class="btn btn-primary">
+            Back to Characters
+        </a>
+    </div>
+</div>
+{% endblock %}