Replace JWT Micropub tokens with revocable opaque tokens

Tokens now store a hashed row in micropub_tokens instead of being
self-contained signed JWTs, so a leaked or unwanted token can actually
be revoked. Since revocation already requires a DB lookup on every
request, JWT's stateless-verification benefit was gone anyway, so this
also drops the lcobucci/jwt dependency entirely.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014625MfkGZ7GVdbqKme4a8L

composer.json

@@ -22,7 +22,6 @@
         "laravel/horizon": "^5.0",
         "laravel/scout": "^10.1",
         "laravel/tinker": "^3.0",
-        "lcobucci/jwt": "^5.0",
         "league/commonmark": "^2.0",
         "league/flysystem-aws-s3-v3": "^3.0",
         "mf2/mf2": "~0.3",