Bring Micropub endpoint closer to the spec

- Detect form-encoded action=... requests, so form-encoded updates work
  and unhandled actions are no longer created as notes
- Default to h-entry when no type is given
- Read form-encoded photos from `photo` rather than `photos`
- Pass `category` through EntryData so bookmark tags are saved
- Accept single values for form-encoded multi-value properties
- Return 403 for insufficient_scope and 401 for invalid tokens
- Return 400 invalid_request for unsupported post types, update
  operations and models instead of reporting them as 500s

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/Http/Responses/MicropubResponses.php

@@ -17,7 +17,7 @@ class MicropubResponses
             'response' => 'error',
             'error' => 'insufficient_scope',
             'error_description' => 'The token’s scope does not have the necessary requirements.',
-        ], 401);
+        ], 403);
     }
 
     /**
@@ -29,7 +29,7 @@ class MicropubResponses
             'response' => 'error',
             'error' => 'invalid_token',
             'error_description' => 'The provided token did not pass validation',
-        ], 400);
+        ], 401);
     }
 
     /**