fix: check response.ok before parsing JSON in fetch calls

Fix JSON parsing errors when server returns non-JSON responses:
- Check response.ok before calling response.json()
- Add fallback error messages using status text
- Apply fix to all fetch calls across 12 components

This prevents 'JSON.parse: unexpected character' errors when
server returns HTML error pages or other non-JSON responses.

src/components/EditTournamentForm.tsx

@@ -56,10 +56,13 @@ export default function EditTournamentForm({ tournament }: EditTournamentFormPro
         }),
       })
 
-      const data = await response.json()
-
       if (!response.ok) {
-        setError(data.error || "Failed to update tournament")
+        try {
+          const data = await response.json()
+          setError(data.error || "Failed to update tournament")
+        } catch {
+          setError(`Failed to update tournament: ${response.status} ${response.statusText}`)
+        }
         setIsLoading(false)
         return
       }