fix: relax CSP to allow SvelteKit bootstrap and Cloudflare edge scripts (#20)

The strict default-src 'self' policy blocked three categories of content
that cannot be handled with build-time hashes:

- SvelteKit's inline bootstrap script in index.html
- Scripts injected by Cloudflare at the edge (Web Analytics, etc.) whose
  content is unknown at build time — once any hash appears in script-src,
  browsers ignore 'unsafe-inline', so hash mode is not a viable escape hatch
- The Cloudflare Insights beacon loaded from static.cloudflareinsights.com
- The style="display:contents" attribute SvelteKit emits on its body wrapper

Adds explicit script-src and style-src directives with 'unsafe-inline' and
the Cloudflare Insights origin/connect-src. The dashboard is already gated
by Cloudflare Access, so CSP here is defence-in-depth rather than the
primary XSS control.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tbjers

dashboard/static/_headers

@@ -2,4 +2,4 @@
   X-Frame-Options: DENY
   X-Content-Type-Options: nosniff
   Referrer-Policy: strict-origin-when-cross-origin
-  Content-Security-Policy: default-src 'self'; img-src 'self' https://avatars.githubusercontent.com; connect-src 'self'; frame-ancestors 'none'; base-uri 'self'; form-action 'self'
+  Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-inline' https://static.cloudflareinsights.com; style-src 'self' 'unsafe-inline'; img-src 'self' https://avatars.githubusercontent.com; connect-src 'self' https://cloudflareinsights.com; frame-ancestors 'none'; base-uri 'self'; form-action 'self'