fix(favicon): use a more robust icon (#371)

* fix(favicon): use a more robust icon

- rocket/gas: proper linecap/linejoin
- drop CSS vars, which aren't supported by all mobile browsers
- drop SVG <defs>, which aren't supported by all SVG editors/tools
- OIF ring: use direct RGB colors rather than HSL colors
- add an *.iso file (generated by svg2ico) for other uses, just in case

The initial SVG favicon, with dark/light color support and CSS variables,
is kept in a separate file.

* fix(website): keep a light/dark banner icon

Author: fabi1cazenave

www/assets/css/theme.css

@@ -266,7 +266,7 @@ blockquote + hr {
 #banner {
   min-height: 50px;
   box-sizing: border-box;
-  background: left var(--main-padding) center no-repeat url(../favicon.svg);
+  background: left var(--main-padding) center no-repeat url(../favicon_light_dark.svg);
   background-size: 50px;
   background-color: var(--bg-banner);
   padding: .5em 0 0.5em calc(var(--main-padding) + 64px);
@@ -483,4 +483,4 @@ code { /* character, digrams, trigrams */
   header + nav li:has(.active) a.active {
     color: var(--fg-banner);
   }
-}
+}