ci: build all five implementations and gate on unexplained failures and regressions

[stormer78]

Adds .github/workflows/conformance.yml. It checks out affinidi-tdk-rs, vta-browser-plugin (tsp-js), affinidi-tsp-go and affinidi-tsp-dart next to the suite, builds every driver from source, and runs the full matrix.

• Triggers: push to main, pull requests, a weekly run, and workflow_dispatch with a ref input for each repo.

• Seed: the run id, so each run uses fresh keys and the report records the seed.

• Gate: a new runner option, --gate known, is non-zero in three cases:

  • a failure that no entry in findings.toml explains (a new disagreement);
  • a failure that matches a finding marked fixed (a regression);
  • a driver that did not build or start.

  make run keeps --gate all.

• findings.toml: three findings are now marked fixed: the XSCS body (#803/#249), the accepter's reply digest (#804) and accept correlation (#250). Findings that match nothing are printed as a note.

• Outputs: the job summary shows the report summary, and the report plus driver logs are uploaded as the conformance-report artifact.

Checked locally against the current merged code: 0 unexplained failures, exit 0. With affinidi-tsp built from a checkout that predates #804, the gate reports REGRESSION (affinidi-accepter-forgets-reply-digest) and exits 1.