Convert pathogens page to use "splat" path component, add error handling; also correct JSDoc

[genehack]

As discussed here and in #1128:

• Convert /pathogens/page.tsx to /pathogens/[[...pathogens]]/page.tsx
• Add in conditional <ErrorMessage> display when [[...pathogens]] has a value, a la how /staging/[[...staging]]/page.tsx currently works
• Correct JSDoc in existing /static-site/app and /static-site/components files to use the format laid out in Standardize JSDoc for TypeScript function parameters #1128