Declare color scheme for themes without them

* Declare argus theme as a light color scheme
* Declare the example theme in the docs as a dark color scheme

Ensures we always have a reasonable fallback regardless of what the user's default OS color scheme is. Otherwise inappropriate fallbacks might be applied, like e.g. dark background color for input fields where the theme is light but the OS/browser is using darkmode, and vice versa.

changelog.d/1088.changed.md

@@ -0,0 +1 @@
+Declared argus-theme as one with the light color scheme in order to awlays have reasonable fallbacks.

changelog.d/1088.fixed.md

@@ -0,0 +1 @@
+Fixed background color in input fields for argus-theme globally.

docs/customization/htmx-frontend.rst

@@ -70,6 +70,7 @@ How to customize the look:
         "dim",
         "autumn",
         { "mytheme": {
+            "color-scheme": "dark",
             "primary": "#009eb6",
             "primary-content": "#00090c",
             "secondary": "#00ac00",

src/argus/htmx/defaults.py

@@ -32,6 +32,7 @@
     "light",
     {
         "argus": {
+            "color-scheme": "light",
             "primary": "#006d91",
             "primary-content": "#d1e1e9",
             "secondary": "#f3b61f",