Fix: add phantom export to prevent empty types.ts compilation error

[rajk93]

fixes #5566

Problem

When using typegen with definitions containing no custom types (only RPC/runtime definitions), the generated types.ts file would be completely empty, causing TypeScript compilation errors when re-exported via export * from './types'.

Solution

Added a phantom export to the tsDef/types.hbs template to ensure the generated file always has at least one export:

  export type PHANTOM_GENERATED = 'generated';

While @jacogr mentioned #5566 (comment) using a timestamped phantom export PHANTOM_GENERATED_<Date.now()> for uniqueness, but here a static phantom export is sufficient because:

• The file is completely auto-generated and overwritten on each build
• No conflict risk since the phantom export is never actually imported or used