Enhance documentation and configuration for static site generator

- Update README for clarity and quick start instructions
- Refine default config.toml with hostname and base path
- Adjust index.md files for consistent heading levels
- Simplify CSS for code block styling and remove unnecessary theme switching
- Refactor SiteConfig to derive full base URL from hostname and base path
- Update MarkdownRenderer to remove light theme handling

docs-gen/defaults/config.toml

@@ -1,7 +1,7 @@
 [site]
 title = "My Docs"
-base_url = "https://example.com"
-base_path = ""
+hostname = "https://example.github.io"
+base_path = "/my-project"
 
 # [[nav]]
 # label = "Guide"
@@ -10,12 +10,10 @@ base_path = ""
 # [[nav]]
 # label = "GitHub"
 # url = "https://github.com/your/repo"
-# icon = "github"
+# icon_svg = '<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M9 19c-5 1.5-5-2.5-7-3m14 6v-3.87a3.37 3.37 0 0 0-.94-2.61c3.14-.35 6.44-1.54 6.44-7A5.44 5.44 0 0 0 20 4.77 5.07 5.07 0 0 0 19.91 1S18.73.65 16 2.48a13.38 13.38 0 0 0-7 0C6.27.65 5.09 1 5.09 1A5.07 5.07 0 0 0 5 4.77a5.44 5.44 0 0 0-1.5 3.78c0 5.42 3.3 6.61 6.44 7A3.37 3.37 0 0 0 9 18.13V22"/></svg>'
 
 [i18n]
-default_lang = "en"
-langs = ["en", "ja"]
+langs = ["en"]
 
 [highlight]
 theme = "base16-ocean.dark"
-theme_light = "InspiredGitHub"