feat(engine): prepare official MCP distribution

[tcballard]

Summary

• publish the native decided-mcp binary as a dedicated crates.io package
• replace the retired Lore/PyPI Registry metadata with io.github.asdecided/core backed by Cargo
• add checksum-pinned, GitHub OIDC Registry publication that is independently retryable
• record the decision, requirements, design, and partial supersession of ADR-039

Release boundary

This prepares the distribution path but does not retroactively rebuild v0.26.0. The first Registry publication should be made from the next patch release so the crate, Git tag, workspace, and Registry record all describe one immutable source commit.

Validation

• official mcp-publisher v1.8.0 validate: passed
• cargo publish --dry-run --locked --allow-dirty -p decided-mcp: passed
• cargo test --locked -p decided-mcp: 20 passed
• decided validate decisions: 440 valid, 0 invalid; OKF v0.2 conformant
• decided relationships decisions --validate: 2,645 checked, 0 issues
• decided sentry decisions --base origin/main: 0 violations
• all workflow YAML parsed locally
• git diff --check: passed

Follow-up after merge

1. prepare the next patch release and update all exact version fields together
2. publish crates through the existing trusted-publishing workflow
3. dispatch the MCP Registry workflow after decided-mcp reaches crates.io

Authored under my direction with Codex.