Move preview button to per-slot in edit form, remove card dropdown

- Preview button always visible next to Variables for each template slot
- Remove \n\n prefix from video_warning default value
- Use conditional {% if video_warning %} with blank line in templates
- Fix all .jinja2 files and inline defaults to match
- Add SVG favicon (camera + notification dot)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/server/src/immich_watcher_server/templates/en/assets_added.jinja2

@@ -9,4 +9,7 @@
     {%- if asset.is_favorite %} ❤️{% endif %}
 {%- endfor %}
 {%- endif %}
+{%- if video_warning %}
+
 {{ video_warning }}
+{%- endif %}