Add GET /companies browse/discover endpoint

Completes the browse/discover set across all four entity types.
Companies have no popularity or date field, so unlike movies/series/
people there's no sort_by choice -- always alphabetical by name.
Filters are company_type (validated against the enum) and country
(a plain ISO 3166-1 code comparison, nothing to validate).

build_company_summary refactored to share row-to-summary logic with
the new list path, same pattern used for movies/series/people.

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

app/api/v1/companies.py

@@ -2,13 +2,13 @@
 
 from __future__ import annotations
 
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, HTTPException, Query, status
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.deps import not_found
 from app.core.database import get_db
 from app.core.security import enforce_rate_limit
-from app.schemas.company import CompanyDetailOut
+from app.schemas.company import CompanyDetailOut, CompanyListOut
 from app.services import company_service
 
 router = APIRouter(
@@ -16,6 +16,24 @@ router = APIRouter(
 )
 
 
+@router.get("", response_model=CompanyListOut)
+async def list_companies(
+    company_type: str | None = Query(
+        None, description="production_company, network, studio, or distributor"
+    ),
+    country: str | None = Query(None, description="ISO 3166-1 alpha-2 country code, e.g. US"),
+    page: int = Query(1, ge=1),
+    page_size: int = Query(20, ge=1, le=50),
+    session: AsyncSession = Depends(get_db),
+) -> CompanyListOut:
+    try:
+        return await company_service.list_companies(
+            session, company_type=company_type, country=country, page=page, page_size=page_size
+        )
+    except company_service.InvalidCompanyFilterError as exc:
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
+
+
 @router.get("/{aurora_id}", response_model=CompanyDetailOut)
 async def get_company(
     aurora_id: str, session: AsyncSession = Depends(get_db)