Add contribution readiness

[N0zoM1z0]

Summary

• Add a local readiness opportunity gate with deterministic pass/warn/block/unknown rule output.
• Add readiness explain for per-check details, evidence references, and remediation.
• Wire readiness into CLI metadata and documentation while keeping evaluation as a pure corpus read.

Why

This gives contributors and agents a final local submit-readiness check before preparing public issue or PR drafts. It surfaces stale evidence, unresolved contradictions, target-thread state, validation state, and collision signals without network access, process execution, or corpus mutation.

Validation

• git diff --check
• GOMAXPROCS=2 go test -p=2 -count=1 ./internal/app ./internal/cli ./internal/corpus
• GOMAXPROCS=2 go test -p=2 -count=1 ./...

Note: golangci-lint is not installed in this local environment, so linter validation is left to CI.

[N0zoM1z0]

LGTM!