fix zola.toml config table scoping bug and JSON-LD safety

[[extra.menu]] silently swallowed ~20 later extra.* keys (posts_page_title,
search_placeholder, show_rss_link, notfound_*, etc.) into the last menu
entry/tag_descriptions table, since TOML absorbs bare keys into the last
open table until a new header appears. show_rss_link was the only visibly
broken one (RSS link missing from homepage); the rest were masked by
matching template defaults.

Also replaced Tera's default() filter with explicit if/else where values
feed into JSON-LD, since default()'s fallback gets escaped in a way `safe`
can't undo. Added author/dateModified to BlogPosting list entries.

templates/base.html

@@ -77,7 +77,7 @@
         {
           "@type": "Person",
           "@id": "{{ config.base_url | safe }}/#author",
-          "name": {{ config.extra.author | default(value="andwati") | json_encode | safe }},
+          "name": {{ config.extra.author | json_encode | safe }},
           "url": "{{ config.base_url | safe }}/about/",
           "sameAs": [
             {% if config.extra.github_url %}"{{ config.extra.github_url | safe }}"{% if config.extra.twitter_url or config.extra.youtube_url %},{% endif %}{% endif %}