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/cordis/src/index.ts

@@ -1,14 +1,14 @@
 /** Core context type and root context implementation. */
-export * from './context'
+export * from './context.ts'
 /** Event bus, dispatch modes, and event augmentation types. */
-export * from './events'
+export * from './events.ts'
 /** Plugin fiber lifecycle, effects, and config validation helpers. */
-export * from './fiber'
+export * from './fiber.ts'
 /** Logger facade, logger service, message, exporter, and formatting types. */
-export * from './logger'
+export * from './logger.ts'
 /** Plugin registry, dependency injection, and plugin entrypoint types. */
-export * from './registry'
+export * from './registry.ts'
 /** Base service class and service lifecycle symbols. */
-export * from './service'
+export * from './service.ts'
 /** Shared internal helpers used by context, services, and plugin fibers. */
-export * from './utils'
+export * from './utils.ts'