fix(api): remove fallback URLs, throw if env var not defined

Per user feedback and Chief Cole direction (Chief_Cole-20251107123442):
- Remove fallback URLs from all API clients
- Throw error if NEXT_PUBLIC_PYTHON_API_URL not defined
- Standardize on NEXT_PUBLIC_PYTHON_API_URL env var across all clients
- Production URL: https://api.playchoo.com (staging/prod share hostname)

Updated files:
- src/lib/api/courts.ts
- src/lib/api/materialisation.ts
- src/lib/api/slot-definitions.ts

All clients now fail fast with clear error if env var missing.
Build tested and passed.

src/lib/api/courts.ts

@@ -14,7 +14,11 @@ import type {
   CourtError,
 } from '@/src/types/courts';
 
-const API_BASE_URL = process.env.NEXT_PUBLIC_API_BASE_URL || 'https://staging.api.playchoo.com';
+const API_BASE_URL = process.env.NEXT_PUBLIC_PYTHON_API_URL;
+
+if (!API_BASE_URL) {
+  throw new Error('NEXT_PUBLIC_PYTHON_API_URL environment variable is not defined');
+}
 
 type ApiResult<T> =
   | { success: true; data: T }

src/lib/api/materialisation.ts

@@ -12,7 +12,11 @@ import type {
   MaterialisationError,
 } from '@/src/types/materialisation';
 
-const API_BASE_URL = process.env.NEXT_PUBLIC_API_BASE_URL || 'https://staging.api.playchoo.com';
+const API_BASE_URL = process.env.NEXT_PUBLIC_PYTHON_API_URL;
+
+if (!API_BASE_URL) {
+  throw new Error('NEXT_PUBLIC_PYTHON_API_URL environment variable is not defined');
+}
 
 type ApiResult<T> =
   | { success: true; data: T }

src/lib/api/slot-definitions.ts

@@ -4,7 +4,11 @@ import type {
   SlotDefinitionError,
 } from '@/src/types/slot-definitions';
 
-const API_BASE_URL = process.env.NEXT_PUBLIC_API_URL || 'https://api.playchoo.com';
+const API_BASE_URL = process.env.NEXT_PUBLIC_PYTHON_API_URL;
+
+if (!API_BASE_URL) {
+  throw new Error('NEXT_PUBLIC_PYTHON_API_URL environment variable is not defined');
+}
 
 type ApiResult<T> =
   | { success: true; data: T }