docs: adopt org logo, favicon, and brand palette (#72)

Match modern-python.org: white wordmark logo top-left, mark favicon, forest-green Material palette.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lesnik512

docs/assets/modern-python-mark.svg

@@ -0,0 +1,17 @@
+/* Brand palette — forest green sampled from the org logo (#356852) */
+:root > * {
+  --md-primary-fg-color:        #356852;
+  --md-primary-fg-color--light: #4a8a6e;
+  --md-primary-fg-color--dark:  #234738;
+  --md-accent-fg-color:         #c98a00;
+}
+
+/* Dark scheme keeps the same brand hue; lighter green for body links so they
+   stay AA-readable on the dark background. */
+[data-md-color-scheme="slate"] {
+  --md-primary-fg-color:        #356852;
+  --md-primary-fg-color--light: #4a8a6e;
+  --md-primary-fg-color--dark:  #234738;
+  --md-accent-fg-color:         #e0a300;
+  --md-typeset-a-color:         #7fb79f;
+}

docs/assets/modern-python-white.svg

@@ -20,6 +20,8 @@ nav:
 
 theme:
   name: material
+  logo: assets/modern-python-white.svg
+  favicon: assets/modern-python-mark.svg
   features:
     - content.code.copy
     - content.action.edit
@@ -30,19 +32,22 @@ theme:
   palette:
     - media: "(prefers-color-scheme: light)"
       scheme: default
-      primary: black
-      accent: pink
+      primary: custom
+      accent: custom
       toggle:
         icon: material/brightness-7
         name: Switch to dark mode
     - media: "(prefers-color-scheme: dark)"
       scheme: slate
-      primary: black
-      accent: pink
+      primary: custom
+      accent: custom
       toggle:
         icon: material/brightness-4
         name: Switch to system preference
 
+extra_css:
+  - css/brand.css
+
 markdown_extensions:
   - toc:
       permalink: true