Clear hook registration API

When hook names are untyped strings with no validation and handler signatures are undocumented, plugin authors must read the host's source code to discover what hooks exist and what arguments their handlers receive. This blocks third-party plugin development, makes the API fragile across upgrades, and guarantees that handler signature mismatches appear only at runtime — not at compile time. ISO 25010 maintainability.modularity depends on well-defined, discoverable interfaces between components; an opaque hook API violates this structurally.

Replace any untyped string-based registration with a generic method that uses a typed hook map. Compile-time enforcement of hook names and handler signatures eliminates an entire class of runtime errors for plugin authors.

interface PluginHooks {
  'before:request': (ctx: RequestContext) => void | Promise<void>;
  'after:response': (ctx: ResponseContext) => void | Promise<void>;
  'on:error': (error: PluginError, ctx: ErrorContext) => void;
}

class HookRegistry {
  on<K extends keyof PluginHooks>(hook: K, handler: PluginHooks[K]): void;
}