Refactor/serve app composition

[DENFNC]

Refactored the Go architecture closer to clean architecture boundaries:

• fixed HTTP app composition by registering routes during dependency setup;
• wired existing auth and trusted proxy middleware at the composition root;
• removed core dependency on the outer pkg package by injecting token generation;
• moved the default HookResponse behavior from the repository layer into the use case layer;
• removed JSON/YAML tags and runtime orchestration types from domain;
• replaced the HTTP handler’s direct dependency on hub.Hub with an EventBroker interface;
• moved serve orchestration types from domain to core.