cli: build partial entries --debug-build-paths arg (#85052)
Add `--debug-build-paths` CLI option to next build for selective route
building. This enables building only specific routes for faster
development and debugging.
### Changes
- Add `--debug-build-paths=<patterns>` CLI option
- Support comma-separated paths and glob patterns
- Filter collected routes after normal file system scanning
- Works with both app router and pages router
### Usage
#### Build specific routes
```sh
next build --debug-build-paths="app/page.tsx,app/dashboard/page.tsx"
next build --debug-build-paths="pages/index.tsx,pages/about.tsx"
```
#### Use glob patterns
```sh
next build --debug-build-paths "app/**/page.tsx"
next build --debug-build-paths "pages/*.tsx"
```
#### Mix both routers
```
next build --debug-build-paths "app/page.tsx,pages/index.tsx"
```
