Bundle CSS with Hugo's Sass feature (#705)

* migrate bootstrap and flags to bundle

* migrated main.css

* migrate navbar.css and plyr

* migrated mulish font and darkreader

* migrated static/css/sections stylesheets

* migrated list page and sidebar styles

* migrated search.html ( nothing to add )

* migration single page styles

* remove duplicated style tags

* migrate notes.  Deleted unused css in static

* migrate 404 css to bundle

* migrate katex styles

* migrate embedpdf styles

* migrated katex css

---------

Co-authored-by: Aaron Qian <aaron@yeet.io>

config.yaml

@@ -0,0 +1,22 @@
+module:
+  mounts:
+  - source: content
+    target: content
+  - source: static
+    target: static
+  - source: layouts
+    target: layouts
+  - source: data
+    target: data
+  - source: assets
+    target: assets
+  - source: i18n
+    target: i18n
+  - source: archetypes
+    target: archetypes
+  - source: ../../node_modules/flag-icon-css/flags
+    target: static/flags
+  - source: ../../node_modules/@fontsource/mulish/files
+    target: static/files
+  - source: ../../node_modules/katex/dist/fonts
+    target: static/fonts