fix: minor fixes and template updates

- seed_demo.py: Change company owner role from "user" to "vendor"
- header.html: Update header partial styling/content
- marketplace.js: Minor JS updates
- marketplace.html: Template updates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/templates/admin/partials/header.html

@@ -24,12 +24,8 @@
             <li class="flex">
                 <button class="rounded-md focus:outline-none focus:shadow-outline-purple"
                         @click="toggleTheme" aria-label="Toggle color mode">
-                    <template x-if="!dark">
-                        <span x-html="$icon('moon', 'w-5 h-5')"></span>
-                    </template>
-                    <template x-if="dark">
-                        <span x-html="$icon('sun', 'w-5 h-5')"></span>
-                    </template>
+                    <span x-show="!dark" x-html="$icon('moon', 'w-5 h-5')"></span>
+                    <span x-show="dark" x-html="$icon('sun', 'w-5 h-5')"></span>
                 </button>
             </li>