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/engine/src/scheduler.ts

@@ -253,7 +253,7 @@ export class Scheduler {
     for (const depId of task.dependencies) {
       const dep = allTasks.find((t) => t.id === depId);
       if (dep && dep.column === "in-review" && dep.worktree) {
-        return `kb/${dep.id.toLowerCase()}`;
+        return `fusion/${dep.id.toLowerCase()}`;
       }
     }
 
@@ -261,7 +261,7 @@ export class Scheduler {
     if (task.blockedBy) {
       const blocker = allTasks.find((t) => t.id === task.blockedBy);
       if (blocker && blocker.column === "in-review" && blocker.worktree) {
-        return `kb/${blocker.id.toLowerCase()}`;
+        return `fusion/${blocker.id.toLowerCase()}`;
       }
     }