feat(heller): add first canonical frame vector candidate

[mdheller]

Summary

Adds the first Heller TritRPC frame-vector candidate for the admitted heller.event_envelope.protobuf.v1 binding.

Included

• fixtures/heller/v1/vectors_hex_heller_event_envelope_protobuf_v1.txt
• fixtures/heller/v1/heller_event_envelope_protobuf_v1.frame_manifest.json
• tools/generate_heller_frame_vector.py
• tools/verify_heller_frame_vector.py
• .github/workflows/validate-heller-frame-vector.yml

Binding covered

• service: heller.v1.Transport
• method: EventEnvelope.Protobuf
• binding id: heller.event_envelope.protobuf.v1
• payload source: fixtures/descriptors/heller/v1/encoded_payload_manifest_v8.json

Scope

This is intentionally one binding only. It makes the first frame-vector candidate reproducible and CI-checkable before expanding to the remaining Heller bindings.

Validation

The new workflow runs:

python tools/verify_heller_frame_vector.py

The verifier regenerates the vector deterministically and checks the vector row plus frame manifest fields.

[mdheller]

Current review posture:

• This PR is mergeable according to GitHub metadata.
• No failing commit status entries are exposed through the connector for the current head.
• This PR is intentionally stacked on feat(heller): add transport admission manifest v0.1 #51 and should not land first.

Recommended landing order:

1. Merge feat(heller): add transport admission manifest v0.1 #51 (transport admission manifest + verifier).
2. Rebase or merge-forward this branch if needed.
3. Then merge feat(heller): add first canonical frame vector candidate #59 as the first canonical Heller frame-vector candidate.