docs: redesign the docs UI — dark-first, instrument-panel identity (#239)

[Nitjsefnie]

Closes #239

Overhauls the docs theme layer to the plan you approved in the issue thread — MkDocs Material kept as the base, dark-mode-first, anchored to the org mark, with a proper landing page, cleaner scannability, and consistent code styling. mkdocs build --strict passes clean (zero warnings).

After (dark — the flagship)

Before → After (dark) · click to expand the before

Before:

Light scheme (before → after)

After (light):

Before (light):

Mobile (after, 390px)

What changed

• Palette — retired indigo/amber for a near-black #0b0c0e / off-white #fcfcfa system with a single accent. The accent is a signal vermilion (#ff5d3b on dark ≈6.4:1, #c4370f on light ≈5.2:1, both AA). It's chosen to read as instrumentation — probes, calibration, pass/fail registers — rather than the generic dev-tool blue or the acid-green everyone reaches for; measurement is what an eval framework is about.
• Dark-first, light-proper. The slate scheme gets the flagship treatment (a masked instrument-glow behind the hero, vermilion selection/focus, deep footer); the light scheme is a real off-white paper design with the same hairline/border vocabulary, not a fallback.
• Typography. Kept the Space Grotesk (display) + Inter (body) pairing but made it a voice: tight display tracking + line-height, comfortable body rhythm, and JetBrains Mono promoted to carry the eyebrows/badges/chips — "anything the machine says is mono."
• Hero. Replaced the abstract Config→Engine diagram with a styled terminal showing the actual loop (pip install → oaeval init → oaeval run → report with scores). The word evaluation in the headline carries the accent.
• Scannability. Feature/metric/provider grids are 1px-bordered cards (borders over heavy shadows) with generous whitespace and a quiet accent-on-hover; motion is a single 0.6s rise, disabled under prefers-reduced-motion.
• Code blocks are consistent, high-contrast, and self-tokenized in the hero so they don't depend on the pygments palette.

Files: docs/stylesheets/extra.css (the bulk), mkdocs.yml (palette), docs/index.md (hero + card grids), docs/overrides/main.html (font link), and the two brand SVGs (see below).

Two things for your call

1. Logo + favicon recolor. The approved plan says "anchored to the org's black/white mark," but the committed logo.svg/favicon.svg were actually indigo — leaving them would drop a spot of the old color into the new palette. I recolored them to the near-black mark with a single vermilion signal dot so the identity is cohesive. This is the one place the PR touches brand assets rather than the theme layer — if you'd rather keep the current mark untouched, it's a two-file revert and the theme works either way. Your call.
2. docs/assets/hero.svg is now unreferenced (the terminal replaced it) but left in place — it's still indigo if you ever reuse it. Happy to delete it if you'd prefer no orphan.

Not touched (flagging, out of scope)

docs/index.md's "Stay connected" links X as x.com/openagentdev while mkdocs.yml's social config uses x.com/openagenthq — a pre-existing content inconsistency, not a theme issue. Left alone; easy follow-up if you want it fixed.

Verification

• pip install mkdocs-material && mkdocs build --strict → built clean, zero warnings (strict turns any broken link/nav/ref into an error).
• Rendered and reviewed in dark, light, and mobile (captures above); both color schemes present in the built output, all :material-*: icons resolve, fonts wired, hero terminal renders.

---

Generated by Claude Opus 4.8 (brief, review), Kimi K3 (implementation).

[github-actions]

🎉 Congratulations @Nitjsefnie!

Your pull request has been successfully merged into main. 🚀

Thank you for contributing to OpenAgentHQ and helping improve the project.

We truly appreciate your contribution and hope to see you back with more amazing PRs!

Happy Open Sourcing! ❤️