Implement CSP Headers to mitigate XSS injection attacks

[perfectly-preserved-pie]

Now that user input is possible, I need to sanitize it. Already implemented server side validation in #358 with bleach but a strict CSP header would be nice as well.

https://web.dev/articles/strict-csp
https://auth0.com/blog/defending-against-xss-with-csp/

[perfectly-preserved-pie]

Pangolin doesn't support custom response headers, so a CSP isn't possible at this time without manually editing the Traefik config. https://github.com/orgs/fosrl/discussions/1939

imma just sit on this

[perfectly-preserved-pie]

https://www.paulsblog.dev/harden-your-website-with-traefik-and-security-headers/

[perfectly-preserved-pie]

https://doc.traefik.io/traefik/reference/routing-configuration/other-providers/docker/