feat: cap custom CSS length and add validation tests

Bound customCSS to 100000 characters on both the client schema and the
server body validation (the server is the enforcement boundary; multer's
1MB field cap was the only limit), regenerate the OpenAPI spec, and add
a validation test suite covering acceptance, clearing, the length cap,
and type rejection.

server/src/api/validation/statusPageValidation.ts

@@ -32,7 +32,7 @@ export const createStatusPageBodyValidation = z
 		showUptimePercentage: booleanCoercion,
 		showAdminLoginLink: booleanCoercion.optional(),
 		showInfrastructure: booleanCoercion.optional(),
-		customCSS: z.string().optional(),
+		customCSS: z.string().max(100000, "Custom CSS must be at most 100000 characters").optional(),
 		removeLogo: z.union([z.literal("true"), z.literal("false")]).optional(),
 		theme: z.enum(StatusPageThemes).optional(),
 		themeMode: z.enum(StatusPageThemeModes).optional(),