Symlink .next build output instead of copying

Replaces copying the .next directory with creating a symlink to preserve internal symlinks, improving compatibility with pnpm. Also removes the root next.config.mjs and adds .next to .gitignore.

Author: hotlong

.gitignore

@@ -34,3 +34,4 @@ next-env.d.ts
 
 # fumadocs
 .source
+.next

next.config.mjs

@@ -61,12 +61,13 @@ export function registerBuildCommand(cli) {
             const destNext = path.join(process.cwd(), '.next');
 
             if (fs.existsSync(srcNext) && srcNext !== destNext) {
-               console.log(`\nMoving .next build output to ${destNext}...`);
+               console.log(`\nLinking .next build output to ${destNext}...`);
                if (fs.existsSync(destNext)) {
                    fs.rmSync(destNext, { recursive: true, force: true });
                }
-               fs.cpSync(srcNext, destNext, { recursive: true });
-               console.log(`Build successfully output to: ${destNext}`);
+               // Use symlink instead of copy to preserve internal symlinks in .next (pnpm support)
+               fs.symlinkSync(srcNext, destNext, 'dir');
+               console.log(`Build successfully linked to: ${destNext}`);
             } else {
                console.log(`\nNo 'out' directory generated in ${src}.`);
                console.log(`This is expected if 'output: export' is disabled.`);