docs: DDEV/Docker repositioning, SEO, brand assets, and content accuracy

[TerrorSquad]

Summary

Repositions the project and docs around the real differentiator — running git hooks inside DDEV/Docker containers — fixes the website SEO basics, adds brand assets, and brings the docs content back in sync with the shipped CLI/config.

Changes

Positioning

• README + docs homepage lead with the container story (the one column no other runner has) instead of "another hook runner"

SEO

• Add sitemap, keyword-rich description, OG/Twitter meta tags
• Fix master → main links (default branch is main)
• lastUpdated + cleanUrls

Brand assets (website/public/)

• Anvil logo (transparent), favicon, 1200×630 social card wired into og:image/twitter:image

Docs accuracy — the content had drifted from the code:

• CLI reference: add missing commands (validate, list, ci, cache clear, update) and all run/doctor/init flags; fix completion shells (pwsh was never supported)
• Config reference: document parallel exec, caching, timeouts, depends_on, env, check-mode, [update], and the full 7-hook list
• Commit policy: correct ticket extraction and add branch-validation / prepare-commit-msg fields
• Env: add SKIP_GROUP_* and FORGE_GLOBAL_CONFIG
• Presets: correct node prettier/eslint extensions
• Add CLAUDE.md and docs/brand-assets.md

Verification

• vitepress build passes (dead-link check clean)
• Doc claims cross-checked against internal/forge/ source (config structs, presets, backend, completion, runner)

🤖 Generated with Claude Code

[TerrorSquad]

Self-review — cross-checked the documented claims against internal/forge/. One accuracy finding:

default_backend default is not "host" (reference/config.md, guide/backends.md)

ResolveBackend (backend.go) treats an omitted default_backend differently from an explicit "host":

• "" (omitted) → auto-detects DDEV if the web container is running, else host
• "host" → always host, auto-detection disabled

The reference table lists the default as "host", which hides the auto-detect behavior, and the backends guide doesn't mention that host opts out of detection. Fixing both.

Everything else verified accurate: full command/flag surface matches app.go, config fields match the structs, presets match presets.go, parallel inheritance matches IsParallelMode, ticket regex matches ticketRegexFor, and the 7-hook list matches supportedHooks. Build passes with the dead-link checker on.