feat(KB-332): rename task prefix from KB to FN and branches from kb/ to fusion/

- Change default task prefix from KB to FN across all packages

- Rename branch naming pattern from kb/{id} to fusion/{id}

- Update all test assertions and fixtures to use new prefixes

- Add changeset for the breaking change

- Resolve merge conflicts in TaskCard.test.tsx touch gesture tests

packages/cli/src/commands/task.ts

@@ -1056,7 +1056,7 @@ export async function runTaskPrCreate(id: string, options: PrCreateOptions = {})
   }
 
   // Build branch name
-  const branchName = `kb/${id.toLowerCase()}`;
+  const branchName = `fusion/${id.toLowerCase()}`;
 
   // Build PR title
   let title: string;