feat(KB-330): rename internal packages from @kb/* to @fusion/*

- Rename @kb/core, @kb/dashboard, @kb/engine to @fusion/* namespace
- Update all import statements across 143+ files to use new package names
- Update workspace dependencies and root package.json references
- Fix bundler configurations (tsup, vite) for new package names
- Update test files and fix typecheck issues
- Add changeset file documenting the package rename

packages/dashboard/app/api.test.ts

@@ -19,7 +19,7 @@ import {
   startPlanningStreaming,
   fetchTasks,
 } from "./api";
-import type { Task, TaskDetail, BatchStatusResponse } from "@kb/core";
+import type { Task, TaskDetail, BatchStatusResponse } from "@fusion/core";
 
 const FAKE_DETAIL: TaskDetail = {
   id: "KB-001",
@@ -1061,7 +1061,7 @@ describe("Git Management API", () => {
 // --- Planning Mode API Tests ---
 
 import { startPlanning, respondToPlanning, cancelPlanning, createTaskFromPlanning } from "./api";
-import type { PlanningQuestion, PlanningSummary } from "@kb/core";
+import type { PlanningQuestion, PlanningSummary } from "@fusion/core";
 
 describe("Planning Mode API", () => {
   const originalFetch = globalThis.fetch;