Use explicit ts specifiers for declarations

Restore explicit .ts relative specifiers in source and enable rewriteRelativeImportExtensions so emitted JS uses .js while declarations keep explicit .ts specifiers. Add a NodeNext declaration-consumer gate to prevent extensionless declaration regressions.

vendor/hmr/src/index.ts

@@ -4,7 +4,7 @@ import { ModuleJob, ModuleLoader, ResolveResult } from '@cordisjs/plugin-loader'
 import type { Include } from '@cordisjs/plugin-include'
 import { ChokidarOptions, FSWatcher, watch } from 'chokidar'
 import { relative, resolve } from 'node:path'
-import { handleError } from './error'
+import { handleError } from './error.ts'
 import type {} from '@cordisjs/plugin-timer'
 import { fileURLToPath, pathToFileURL } from 'node:url'
 import { createRequire } from 'node:module'