docs(marketing): sharpen positioning — lead with trust, not "expert"

[criptogus]

The old copy said the same thing every prompt-engineering product says ("turn your AI into an expert"). It hid the actual moats and left the reader guessing who the product is for.

New positioning leads with the proof, not the promise:

• Hero now states the differentiator in one sentence — "benchmarked against an adversarial suite, cryptographically signed at release, and scored on real production telemetry"
• Headline rotates the public-facing risk surface ("production / compliance / PHI data / your customers / real money") instead of abstract jobs
• WhatIsThis section replaced ("Skills / Playbooks / Souls / Guardrails" generic) with the actual moats (Adversarial harness / Signed Trust Score / Verticalized Souls / One MCP endpoint)
• New WhoItsFor section with five concrete personas (eng leads, security, regulated teams, solo builders, authors) each pointing at the right marketplace filter, vertical, or bounty board
• Trust metrics row replaced vanity counts (4,218 experts / 91k upgraded) with provable claims (100% signed, 5 verticals, 7 injection classes blocked, 30s MCP setup)
• Meta tags + JSON-LD updated to match new positioning
• README "Why" section rewritten around proprietary adversarial harness, Ed25519 signing, public Trust Score, verticalized Souls
• README adds "Who it's for" table mirroring landing personas

What does this PR add?

Type

• New package (skill / playbook / soul / guardrail)
• Improvement to an existing package (bumped version)
• Platform code or docs

Checklist (for content PRs)

• Filename matches slug and the type's folder
• At least 2 worked examples (skills) — realistic input + exact expected output
• Original work, public-domain, or properly attributed; no secrets / PII
• bun run validate:content passes locally
• I've read CONTRIBUTING.md and agree to license under Apache-2.0 (code) / CC-BY-SA-4.0 (content)

Notes for reviewers