feat: move NextBuilder to @workflow/next package

Moves NextBuilder from @workflow/cli to @workflow/next package, establishing
proper package boundaries where framework-specific builders live in their
respective framework integration packages.

Changes:
- Moved NextBuilder from @workflow/cli to @workflow/next
- Added @workflow/builders and watchpack dependencies to @workflow/next
- Updated runtime re-export to use @workflow/core/dist/runtime directly
- Removed direct dependency on @workflow/cli from @workflow/next

This aligns the Next.js builder with the Nitro builder pattern (which already
lives in @workflow/nitro), creating consistent package organization.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: pranaygp

packages/next/package.json

@@ -28,13 +28,15 @@
   },
   "dependencies": {
     "@swc/core": "1.11.24",
-    "@workflow/cli": "workspace:*",
+    "@workflow/builders": "workspace:*",
     "@workflow/core": "workspace:*",
-    "@workflow/swc-plugin": "workspace:*"
+    "@workflow/swc-plugin": "workspace:*",
+    "watchpack": "2.4.4"
   },
   "devDependencies": {
     "@workflow/tsconfig": "workspace:*",
     "@types/node": "catalog:",
+    "@types/watchpack": "2.4.4",
     "next": "15.5.3"
   },
   "peerDependencies": {

packages/next/src/index.ts

@@ -1,4 +1,4 @@
-import { NextBuilder } from '@workflow/cli/dist/lib/builders/next-build';
+import { NextBuilder } from './next-builder.js';
 import type { NextConfig } from 'next';
 
 export function withWorkflow({