XY-876 Dogfood and release Decodex v0.2 Loop Engineering candidate

[yvette-carlisle]

Summary

• Bump Decodex workspace version and lockfile from 0.1.0 to 0.2.0.
• Add the v0.2.0 Loop Engineering release-readiness runbook and index entry.
• Correct migration-guide focused test commands to current targeted filters.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make test: 1035 passed, 1 skipped
• cargo make check: 1035 passed, 1 skipped
• cargo test -p decodex review --all-features -- --test-threads=1: 166 passed
• cargo test -p decodex config --all-features -- --test-threads=1: 60 passed
• cargo test -p decodex loop_scenarios --all-features -- --test-threads=1: 2 passed
• cargo test -p decodex normal_prompts --all-features -- --test-threads=1: 2 passed
• cargo test -p decodex dry_run --all-features -- --test-threads=1: 11 passed
• cargo test -p decodex recovery --all-features -- --test-threads=1: 33 passed
• cargo run -p decodex --bin decodex -- probe stdio://: PROBE_OK
• cargo run -p decodex --bin decodex -- status --live --json: XY-876 retained attention, review checkpoint pending
• cargo run -p decodex --bin decodex -- run --dry-run: planned XY-876 attempt 2 on the retained worktree
• git diff --check

Review

• Independent read-only review found XY876-RR-001: release checklist ran check before canonicalization.
• Fixed by ordering the runbook gate as WORKFLOW.md canonicalize commands first, then verify, then final cargo make check on the final tree.
• Re-ran cargo make check after the fix: 1035 passed, 1 skipped.

Release note

This PR prepares the v0.2.0 tag contract and release-readiness evidence checklist. It does not publish or tag v0.2.0. The runbook still requires a real standard-review dogfood lane with inspectable Decodex Review checkpoint before tagging.