feat: add @quartz-themes/core to config and templates

Add disabled theme entry to default config and default/blog templates.
Migrate obsidian and ttrpg templates from git-based quartz-themes source
to npm @quartz-themes/core package.

quartz.config.default.yaml

@@ -100,6 +100,11 @@ plugins:
     order: 92
   - source: "@quartz-community/quartz-fonts"
     enabled: true
+  - source: "@quartz-themes/core"
+    enabled: false
+    options:
+      theme: tokyo-night
+      mode: both
   - source: "@quartz-community/remove-draft"
     enabled: true
   - source: "@quartz-community/explicit-publish"