fix(skills): canonical host-accurate install copy, keep 0.1.3 SSOT frontmatter

[chrisjleal]

What

Restores the canonical skills/ in this repository to the host-accurate install copy while keeping the 0.1.3 frontmatter SSOT.

• skills/proofable-setup/SKILL.md: adopts the host-accurate sign-in copy ("there is no universal Connect button...").
• skills/proofable-trust-workflow/references/setup.md: same.
• plugins/proofable-mcp/skills/**: regenerated by scripts/sync-plugin-skills.mjs.

The 0.1.3 metadata: frontmatter block is preserved, so validate-manifest-ssot.mjs still passes.

Why

proofable/sdk main already publishes this exact copy (0.1.4). The SDK Release workflow enforces cross-repository skill parity with --require, so the SDK cannot publish while this repository's canonical skills/ carries the older Connect copy.

The previous approach (PR #1) branched before ab667b6 ("align skill frontmatter to 0.1.3 SSOT and guard it"), so it reverted that newer frontmatter guard and cannot merge cleanly. This change is based on current main and carries only the copy delta.

Verification

• scripts/sync-plugin-skills.mjs --check --plugin-only - in sync
• scripts/sync-plugin-skills.mjs --check (cross-repo vs @proofable/sdk main) - in sync
• npm test - validation passed, including Manifest SSOT across 3 plugin manifests, 3 marketplaces, package.json and the canonical skills

Supersedes

Supersedes #1, which is built on a stale base and drops the frontmatter guard. Do not merge #1; merge this instead.

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