Servers like wafrn return AP JSON without @context, causing Fedify's
JSON-LD processor to reject the document. Strategy 1b in resolveAuthor
does a direct signed GET, extracts attributedTo/actor from plain JSON,
then resolves the actor via lookupWithSecurity.
Also: _loadRsaPrivateKey now imports with extractable=true (required
by Fedify's signRequest), and loadRsaKey is wired through to all
Mastodon API interaction helpers.