feat: consume gates in advance-pipeline smoke path

[apcjoaofilho]

What

Adds the first gate-consuming scripts/advance-pipeline.py implementation and a greenfield smoke fixture.

Why

Completes the next M6/M5 slice after PR #26: gates now have a script consumer, and examples/greenfield-cli-tool proves a RESEARCH to SPEC transition updates both STATE.json and STATUS.md.

How

• Reads STATE.json, STATUS.md, templates/gates/<phase>.yaml, and .sdd/gates/<phase>.json evidence.
• Validates boolean, enum, and integer gate checks without runtime dependencies.
• Advances phase only when evidence passes.
• Updates STATE.json and appends a STATUS.md history row on pass.
• Increments retry count and escalates to BLOCKED after repeated gate failures.
• Adds focused tests under tests/scripts/ and a greenfield example fixture.

Scope check

• PR addresses one implementation slice
• No scope added outside PLAN.md
• Script has tests in tests/scripts/
• Templates remain validated by existing CI
• CHANGELOG updated

Notes

Local shell commands are still blocked in this environment by bwrap: loopback: Failed RTM_NEWADDR: Operation not permitted, so validation is expected from CI.