Add exercise numbers, image uploads, version display, session resume, and training sparklines

- Exercise number (UF#): optional field on exercises, displayed in cards, training, and sets
- Import training plan numbers via migration 005 (UPDATE by name)
- Exercise images: JPG upload with multi-image support per exercise (migration 006)
- Version endpoint (GET /api/v1/version) with ldflags injection in Makefile and Dockerfile
- Version displayed on settings page
- Session resume: GET /api/v1/sessions/active endpoint, auto-resume on training page load
- Block new session while one is active (409 Conflict)
- e1RM sparkline chart per exercise during training (Epley formula)
- Fix CORS: add X-User-ID to allowed headers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/SettingsPage.tsx

@@ -1,14 +1,17 @@
 import { useEffect, useState } from 'react';
 import { useUserStore } from '../stores/userStore';
+import { api } from '../api/client';
 
 export function SettingsPage() {
   const { users, activeUser, setActiveUser, fetchUsers, createUser, deleteUser } =
     useUserStore();
   const [newName, setNewName] = useState('');
   const [loading, setLoading] = useState(false);
+  const [version, setVersion] = useState('');
 
   useEffect(() => {
     fetchUsers();
+    api.version().then((v) => setVersion(v.version)).catch(() => {});
   }, [fetchUsers]);
 
   async function handleCreate(e: React.FormEvent) {
@@ -90,6 +93,10 @@ export function SettingsPage() {
           </button>
         </form>
       </section>
+
+      {version && (
+        <p className="text-xs text-gray-600 pt-4">Version {version}</p>
+      )}
     </div>
   );
 }