Deploy docs site with Hugo and GitHub Actions

[oschwald]

Summary

Migrates the docs site from Jekyll on gh-pages to a Hugo build deployed
via GitHub Actions. All CSS is now inlined in the layout template — no
external CDN dependencies.

• Hugo site lives under docs/ on main and mounts the existing
  doc/libmaxminddb.md and doc/mmdblookup.md as content, keeping the
  source of truth in one place
• A small pill nav at the top of each page lets readers move between the
  two docs
• .github/workflows/pages.yml builds with mise run build-docs and
  deploys via the GitHub Actions Pages environment
• dev-bin/release.sh no longer clones gh-pages or regenerates the
  index/mmdblookup Jekyll pages

Same design as MaxMind-DB PR #221: Charter serif body text, forest-green
accent on field-name headings, hover # anchor links.

Preview locally with mise run serve-docs.

For STF-448.

Post-merge steps

1. Apply Terraform in mm_website to switch Pages source from
   gh-pages to GitHub Actions
2. Verify the site at https://maxmind.github.io/libmaxminddb/ and
   https://maxmind.github.io/libmaxminddb/mmdblookup/
3. Delete the legacy gh-pages branch

Test plan

• mise run build-docs succeeds with no warnings
• Both index.html and mmdblookup/index.html render with correct
  titles and working pill-nav
• grep -r static-gh docs/ returns nothing
• Build job passes in CI (deploy only runs on main)
• After merge + Terraform apply, verify the live site renders correctly

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request migrates the project documentation from Jekyll to Hugo. It removes the manual documentation generation logic from the release script, adds Hugo configuration and layouts, and introduces mise tasks for building and serving the site. Review feedback focuses on refining the Hugo implementation, specifically restoring descriptive page titles lost during the migration, improving title tag logic, utilizing link titles in navigation, and pinning the Hugo version in the configuration for better build reproducibility.

[gemini-code-assist]

The migration to Hugo has resulted in the loss of descriptive page titles that were previously provided in the Jekyll front matter. Currently, Hugo defaults to using the filename (e.g., "mmdblookup") as the title. You can restore the descriptive titles (and optionally provide shorter link titles for the navigation) using Hugo's cascade feature in the configuration file.

Suggested change

	[[cascade]]
	layout = "default"
	[[cascade]]
	layout = "default"
	[[cascade]]
	[cascade._target]
	path = "/_index.md"
	title = "libmaxminddb - a library for working with MaxMind DB files"
	linkTitle = "libmaxminddb"
	[[cascade]]
	[cascade._target]
	path = "/mmdblookup.md"
	title = "mmdblookup - a utility to look up an IP address in a MaxMind DB file"
	linkTitle = "mmdblookup"

[gemini-code-assist]

To support descriptive titles for the home page (set via configuration or front matter), the title tag should check for .Title before falling back to .Site.Title.

Suggested change

	<title>{{ if .IsHome }}{{ .Site.Title }}{{ else }}{{ $title }} | {{ .Site.Title }}{{ end }}</title>
	<title>{{ if .IsHome }}{{ or .Title .Site.Title }}{{ else }}{{ $title }} | {{ .Site.Title }}{{ end }}</title>

[gemini-code-assist]

Using .LinkTitle in the navigation allows for shorter labels in the pill nav while maintaining descriptive titles for the browser tab. This works in conjunction with the cascade settings in hugo.toml.

Suggested change

	<a href="{{ .Site.Home.RelPermalink }}"{{ if .IsHome }} class="active"{{ end }}>{{ .Site.Title }}</a>
	{{ range .Site.RegularPages }}
	<a href="{{ .RelPermalink }}"{{ if eq $.RelPermalink .RelPermalink }} class="active"{{ end }}>{{ or .Title .File.BaseFileName }}</a>
	{{ end }}
	<a href="{{ .Site.Home.RelPermalink }}"{{ if .IsHome }} class="active"{{ end }}>{{ or .Site.Home.LinkTitle .Site.Title }}</a>
	{{ range .Site.RegularPages }}
	<a href="{{ .RelPermalink }}"{{ if eq $.RelPermalink .RelPermalink }} class="active"{{ end }}>{{ or .LinkTitle .Title .File.BaseFileName }}</a>
	{{ end }}

[gemini-code-assist]

It is recommended to pin the Hugo version to a specific version (e.g., the one currently in the lock file) to ensure build reproducibility across different environments and CI. Using latest can lead to unexpected build failures if a new version of Hugo introduces breaking changes.

Suggested change

	hugo = "latest"
	hugo = "0.161.1"