Add sidebar Tags section to offline mode

Offline mode had tag chips and per-task tag assignment, but was
missing the dashboard sidebar's Tags section entirely: filtering the
task list by tag, per-tag task counts, and tag create/rename/delete.
Ports that section over (reusing the same tag modal pattern as the
online create/edit flow), combinable with the existing status filters
the same way it works online.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/offline_tasks.html

@@ -80,6 +80,17 @@
                     </a>
                 </nav>
             </div>
+
+            <div class="sidebar-section">
+                <div class="sidebar-section-title">Tags</div>
+                <nav class="sidebar-nav" id="offline-tag-nav"></nav>
+                <button type="button" class="sidebar-add-btn" id="offline-add-tag-btn">
+                    <svg style="width: 14px; height: 14px;" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+                        <path d="M12 5v14M5 12h14"/>
+                    </svg>
+                    Add Tag
+                </button>
+            </div>
         </aside>
 
         <!-- Main Task Pane -->
@@ -116,6 +127,39 @@
         <div class="mobile-overlay" id="mobile-overlay" onclick="closeOfflineMobileMenus()"></div>
     </div>
 
+    <!-- Tag Edit/Create Modal (outside app-layout for proper fixed positioning) -->
+    <div class="modal-backdrop" id="tag-modal-backdrop">
+        <div class="modal" onclick="event.stopPropagation()">
+            <div class="modal-header">
+                <h2 class="modal-title" id="tag-modal-title">New Tag</h2>
+                <button type="button" class="modal-close" id="tag-modal-close-btn">
+                    <svg style="width: 20px; height: 20px;" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+                        <path d="M18 6L6 18M6 6l12 12"/>
+                    </svg>
+                </button>
+            </div>
+            <form id="tag-edit-form">
+                <div class="form-group">
+                    <label class="form-label" for="tag-modal-name">Name</label>
+                    <input type="text" class="form-input" id="tag-modal-name" required placeholder="Tag name">
+                </div>
+                <div class="form-group">
+                    <label class="form-label">Color</label>
+                    <div class="color-presets" id="tag-modal-color-presets"></div>
+                    <div class="color-custom-row">
+                        <label class="color-custom-label">Custom:</label>
+                        <input type="color" id="tag-modal-color" class="color-custom-input" value="#3b82f6">
+                    </div>
+                </div>
+                <div class="modal-actions">
+                    <button type="button" class="btn btn-secondary" id="tag-modal-cancel-btn">Cancel</button>
+                    <button type="button" class="btn btn-danger" id="tag-modal-delete-btn" style="display: none;">Delete</button>
+                    <button type="submit" class="btn btn-primary" id="tag-modal-submit-btn">Create</button>
+                </div>
+            </form>
+        </div>
+    </div>
+
     <script src="{% static 'js/offline-db.js' %}"></script>
     <script src="{% static 'js/offline-tasks.js' %}"></script>
 </body>

templates/sw.js

@@ -1,4 +1,4 @@
-{% load static %}const CACHE_NAME = 'keepitgoing-shell-v5';
+{% load static %}const CACHE_NAME = 'keepitgoing-shell-v6';
 const OFFLINE_URL = '{% url "offline" %}';
 const OFFLINE_TASKS_URL = '{% url "offline-tasks" %}';