Fix backend deps and apply theme to all Cancel buttons

- Pin bcrypt==3.2.2 to fix passlib bcrypt backend detection error
- Add email-validator==2.2.0 required by Pydantic EmailStr
- Add btn-sm class to Cancel buttons in Admin, Dashboard, Log, Schedule views

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

frontend/src/views/DashboardView.vue

@@ -77,7 +77,7 @@
             </select>
           </div>
           <div class="dialog-actions">
-            <button @click="showStartDialog = false">Cancel</button>
+            <button class="btn-sm" @click="showStartDialog = false">Cancel</button>
             <button class="btn-primary" @click="startSession">Start</button>
           </div>
         </div>