Add GET /genres directory endpoint

GET /movies and GET /series accept a genre filter (an Aurora genre id),
but nothing exposed what those ids actually are -- genres otherwise
only ever appear embedded in a movie/series response's own genres
list. This is the resolve-by-name-first-then-filter step the frontend
needs to build real genre browsing.

No filter, no sort_by -- always alphabetical by name, same pattern as
collections/companies (genres have no categorical field or popularity/
date to sort by). page_size defaults to 50 (max 200) rather than the
20/50 used elsewhere, since genres are a small, fixed reference set
(TMDb has ~19-20 total) a client typically wants in full for a filter
dropdown, not paginated like a catalog of millions of movies.

Also fixed two stale "behind Traefik" mentions in app/main.py's module
docstring while touching this file, left over from the earlier
cPanel/host-webserver deployment change.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

app/main.py

@@ -1,7 +1,8 @@
 """Aurora Core FastAPI application factory.
 
 Stateless by design (section 1): nothing here holds request-scoped state in
-process memory, so any number of API replicas can run behind Traefik.
+process memory, so any number of API replicas can run behind a reverse
+proxy without sticky sessions.
 """
 
 from __future__ import annotations
@@ -25,6 +26,7 @@ from app.api.v1 import (
     collections,
     companies,
     episodes,
+    genres,
     health,
     movies,
     people,
@@ -174,4 +176,5 @@ app.include_router(episodes.router, prefix=API_V1_PREFIX)
 app.include_router(people.router, prefix=API_V1_PREFIX)
 app.include_router(collections.router, prefix=API_V1_PREFIX)
 app.include_router(companies.router, prefix=API_V1_PREFIX)
+app.include_router(genres.router, prefix=API_V1_PREFIX)
 app.include_router(admin.router, prefix=API_V1_PREFIX)