* rss: full URL in RSS link; use request Host in URLs
Full URL syntax on request from third parties.
Using the actual request host should fix issues with non-bsky-production
deployments. It is HTTPS-only, so doesn't work perfectly for local dev.
* rss: make /profile/{handle}/rss an HTTP redirect
Motivation is easier discoverability of RSS feed.
* web: initial implementation of profile RSS feed
* re-work RSS feed to use DID in URL, not handle
Shouldn't have RSS feeds break when folks change handle.
* rss: tweak XML
