🎨 Adopt dark-only theme aligned with axone.xyz

[ccamel]

Task

Update the documentation site (Docusaurus) to use a dark-only theme, visually consistent with https://axone.xyz.

Reference color palette

Extracted from axone.xyz for consistent styling:

• Background: #191716
• Text (primary): #d9d9d9
• Text (muted): #959595
• Primary accent: #ff773d
• Brand blue: #044da2
• Success: #13ce66
• Accent alt / focus: #00ff95
• Danger (background use): #661d1d

Note: Do not modify brand assets (logo, favicon, social preview images) — these are handled in a separate issue.

Reference typography

For readability and alignment with axone.xyz:

• Body text: Inter (fallback: Helvetica, Arial, sans-serif)
• Headings: Montserrat (fallback: Helvetica, Arial, sans-serif)

Requirements

• Enforce dark-only mode by removing the light/dark theme toggle in Docusaurus.
• Apply the reference color palette consistently across:
  • Backgrounds, text, links, buttons, and other UI components.
  • Code blocks (using Prism.js) and admonitions (e.g., note, tip, warning).
  • Mermaid diagrams (via Docusaurus Mermaid plugin or equivalent).
• Use the specified typography: Inter for body text, Montserrat for headings.
• Ensure readability of long-form documentation pages in dark mode.
• If uncertainties or design conflicts arise (e.g., unclear styling for a component), post questions in this issue rather than making assumptions.
• Test rendering across modern browsers (Chrome, Firefox, Safari).

Acceptance criteria

• Documentation loads in dark mode by default with no option to switch to light mode.
• All UI elements (backgrounds, text, links, buttons), code blocks, admonitions, and Mermaid diagrams use the specified color palette and typography.
• Long-form documentation pages are comfortable to read in dark mode (e.g., no eye strain from low contrast or overly bright elements).
• All text, code blocks, and interactive elements pass WCAG 2.1 AA contrast checks, with contrast ratios of at least 4.5:1 for normal text and 3:1 for large text.
• Documentation renders consistently across modern browsers (Chrome, Firefox, Safari).
• No visual artifacts (e.g., light backgrounds in code blocks or diagrams) remain.
• Brand assets (logo, favicon, social preview images) remain unchanged.

Out of scope

• Modifying logos, favicons, or social preview images.
• Changing documentation content, structure, or layout.
• Implementing features unrelated to the dark theme (e.g., PWA functionality).