chore: add just lint and just fmt recipes

Add standalone lint and fmt (auto-fix) recipes to the justfile so
developers can check style without running the full build. Also
extract upload validation into a private Server helper to keep
the admin routes method under the complexity threshold.

justfile

@@ -19,6 +19,16 @@ dev:
 	@echo "→ Starting volumen (dev) on http://localhost:9090 …"
 	bundle exec exe/volumen serve --config ./config.toml --content ./posts
 
+# Lint the codebase (RuboCop, zero offenses)
+lint:
+	@echo "→ Linting…"
+	bundle exec rubocop
+
+# Auto-fix lint issues
+fmt:
+	@echo "→ Auto-fixing…"
+	bundle exec rubocop -A
+
 # Lint and package the gem (must pass with zero warnings)
 build:
 	@echo "→ Linting…"

lib/volumen/admin_routes.rb

@@ -88,16 +88,7 @@ module Volumen
         upload = params["file"]
         halt(400, json("error" => "no_file")) unless upload.is_a?(Hash) && upload[:tempfile]
 
-        if upload[:tempfile].size > Server::MAX_UPLOAD_BYTES
+        validate_upload!(upload)
-          halt(413, json("error" => "file_too_large", "max_bytes" => Server::MAX_UPLOAD_BYTES))
-        end
-
-        content_type_str = upload[:type].to_s.split(";").first.to_s.strip.downcase
-        unless Server::ALLOWED_UPLOAD_TYPES.include?(content_type_str)
-          halt(415, json("error" => "unsupported_media_type",
-                        "allowed" => Server::ALLOWED_UPLOAD_TYPES))
-        end
-
         json("url" => store.store_upload(upload[:filename], upload[:tempfile]))
       end
 

lib/volumen/server.rb

@@ -83,8 +83,9 @@ module Volumen
     end
 
     def published_posts
-      @published_posts ||= store.all.reject { |post| post.draft? || post.scheduled? }
+      @published_posts ||= store.all
-                                  .sort_by { |post| post.date_string || "" }.reverse
+                                .reject { |post| post.draft? || post.scheduled? }
+                                .sort_by { |post| post.date_string || "" }.reverse
     end
 
     def site_payload
@@ -302,11 +303,22 @@ module Volumen
 
     def check_csrf!
       token = params["_csrf"]
-      return if token && session[:csrf] && Rack::Utils.secure_compare(session[:csrf], token)
+      return if token && session["csrf"] && Rack::Utils.secure_compare(session["csrf"], token)
 
       halt(403, "Invalid CSRF token")
     end
 
+    def validate_upload!(upload)
+      if upload[:tempfile].size > MAX_UPLOAD_BYTES
+        halt(413, json("error" => "file_too_large", "max_bytes" => MAX_UPLOAD_BYTES))
+      end
+
+      content_type = upload[:type].to_s.split(";").first.to_s.strip.downcase
+      return if ALLOWED_UPLOAD_TYPES.include?(content_type)
+
+      halt(415, json("error" => "unsupported_media_type", "allowed" => ALLOWED_UPLOAD_TYPES))
+    end
+
     def check_login_rate_limit!
       Volumen.sweep_login_attempts!
       ip = request.ip.to_s