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/engine/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "@kb/engine",
+  "name": "@fusion/engine",
   "version": "0.1.0",
   "type": "module",
   "exports": {
@@ -21,7 +21,7 @@
     "test": "vitest run"
   },
   "dependencies": {
-    "@kb/core": "workspace:*",
+    "@fusion/core": "workspace:*",
     "@mariozechner/pi-ai": "^0.62.0",
     "@mariozechner/pi-coding-agent": "^0.62.0"
   },