feat: add fusion for multi-run sessions

Adds Run fusion for multi-run-like sessions
Combines sibling outputs into a new fusion session
Adds configurable Fusion prompts in Magic Prompts settings

packages/ui/src/components/sections/magic-prompts/MagicPromptsPage.tsx

@@ -140,6 +140,14 @@ const PROMPT_PAGE_MAP: Record<string, PromptPageConfig> = {
       { id: 'session.review.instructions', titleKey: 'settings.magicPrompts.page.block.instructions' },
     ],
   },
+  'session.fusion': {
+    titleKey: 'settings.magicPrompts.page.group.sessionFusion.title',
+    descriptionKey: 'settings.magicPrompts.page.group.sessionFusion.description',
+    blocks: [
+      { id: 'session.fusion.visible', titleKey: 'settings.magicPrompts.page.block.visiblePrompt' },
+      { id: 'session.fusion.instructions', titleKey: 'settings.magicPrompts.page.block.instructions' },
+    ],
+  },
 };
 
 const hasOwn = (input: Record<string, string>, key: string) => Object.prototype.hasOwnProperty.call(input, key);

packages/ui/src/components/sections/magic-prompts/MagicPromptsSidebar.tsx

@@ -47,6 +47,7 @@ export const MagicPromptsSidebar: React.FC<MagicPromptsSidebarProps> = ({ onItem
         items: [
           { id: 'session.summary', titleKey: 'settings.magicPrompts.sidebar.item.sessionSummary' },
           { id: 'session.review', titleKey: 'settings.magicPrompts.sidebar.item.sessionWorkspaceReview' },
+          { id: 'session.fusion', titleKey: 'settings.magicPrompts.sidebar.item.sessionFusion' },
         ],
       },
     ] as const;