docs: add tiered marketing site with docs under /docs/

[wesm]

msgvault.io previously served only the reference docs at the domain root, with no page that says what msgvault is or where it is going. This gives the site the same three-tier shape as the other kenn-io project sites, in a carbon monochrome design matched to the existing msgvault mark:

• / — marketing page: msgvault as the system of record for your communications and relationships. Covers every shipped source, the people layer, hybrid search, the Docbank-backed document and visual lanes, the interface surfaces, and the verify → stage → gated-execute → restore deletion model. An install matrix offers the macOS/Linux script, Homebrew, and Windows PowerShell journeys with per-row copy buttons.
• /guide/ — a nine-stop archive lifecycle tour (Capture → Preserve → Resolve → Curate → Understand → Search → Analyze → Act → Own), each stop pairing copy with a hand-drawn SVG diagram or a capture from the reviewed Enron fixture, and deep-linking into the docs.
• /docs/ — the existing Zensical docs, now built into a subpath by the same vercel-build.sh.

The Directory/Reviews/Settings workspaces from #705 appear only as a labelled "in development" placeholder; nothing unshipped is claimed as current. Both new tiers ship exact Markdown twins (/index.md, /guide.md) and an llms.txt index for machine readers.

Moving the docs under /docs/ changes every published URL, so vercel.json adds permanent redirects for all legacy paths (top-level pages, usage/, guides/, architecture/, search/, and the hydrated asset directories), and absolute internal links in the docs sources now carry the /docs/ prefix. check_built_site.py validates the combined site and check_vercel_redirects.py enforces the full redirect table; bash scripts/check-docs.sh passes end to end.

🤖 Generated with Claude Code

[roborev-ci]

roborev: Combined Review (2a86f81)

Verdict: High-risk deployment and credential-exposure issues require fixes before merge.

Critical

None.

High

• docs/vercel-build.sh:14-21 — The build requires ../website, but the documented Vercel deployment runs from docs/; that sibling directory will be outside the remote deployment root and unavailable during the build. Include website/ in the deployment context or move/package it under docs/.

Medium

• docs/vercel-build.sh:15-21 — The script recursively copies the entire website tree without filtering dotfiles or credential patterns such as client_secret*.json, token*.json, .pem, or .env. Accidentally placed local credentials could become publicly downloadable. Copy an explicit allowlist or apply the same filtering used by zensical-docs.sh, and make the final inventory check part of vercel-build.sh.

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Reviewers: 2 done | Synthesis: codex, 9s | Total: 7m45s

[roborev-ci]

roborev: Combined Review (55028c1)

Verdict: One medium-severity issue requires attention; no critical or high-severity issues found.

Medium

• Sitemap is not deployed at the standard root path
  Location: docs/vercel-build.sh:10, docs/overrides/sitemap.xml:4-21
  The sitemap is generated under site/docs/sitemap.xml, leaving the deployed site without /sitemap.xml. Copy or rewrite it to the Vercel output root and validate the route.

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Reviewers: 2 done | Synthesis: codex, 6s | Total: 10m58s

[wesm]

cc @salmonumbrella

[roborev-ci]

roborev: Combined Review (adbee42)

Verdict: One medium-severity issue found; no high or critical issues.

Medium

• docs/index.md:12, Makefile:354 — make docs-serve serves generated docs at the server root, while links and assets target /docs/..., causing local navigation and images to return 404s. Serve the site under /docs/ or use local-root paths during development.

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Reviewers: 2 done | Synthesis: codex, 9s | Total: 8m30s

[roborev-ci]

roborev: Combined Review (8f7efb7)

Verdict: High-risk deployment issue and a Medium-severity local documentation serving issue require attention.

High

• docs/vercel-build.sh:18-25 — Deployment runs from docs/, but the builder requires the sibling website/ directory, which may be absent from the Vercel upload and cause deployment failure. Include website/ in the project root/upload or move its sources under docs/.

Medium

• docs/zensical.toml:3, Makefile:392-394 — Documentation links and assets use /docs/..., but docs-serve serves only Zensical output at the root and does not build the tiered site. Local navigation and images may resolve to nonexistent paths. Serve the combined output locally or mount the docs tier at /docs/.

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Reviewers: 2 done | Synthesis: codex, 8s | Total: 8m49s

[roborev-ci]

roborev: Combined Review (b0e7260)

Verdict: No Medium, High, or Critical issues found.

All reviewers found no actionable findings at or above Medium severity.

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Reviewers: 2 done | Synthesis: codex, 9s | Total: 7m51s

[wesm]

I am going to merge, but not deploy this, so I will revise the details before releasing v0.20.0 cc @salmonumbrella