[boeboe]

Rolls out ADR-0012 (own-stack images) to sunspec-interop, following engineering/docs/own-stack-rollout.md with modbus-interop as the reference.

What changes

• own/go-sunspec/ (Dockerfile, Makefile, README, Go adapter + tests) and .github/workflows/own-go-sunspec.yml (copied from modbus-interop's): manual only, builds ghcr.io/otfabric/sunspec-interop-otfabric from the latest go-sunspec release, tests it against the references and self-tests of the latest harness tag on amd64 and arm64, publishes :<go-sunspec version> and :latest from main only. Not in the release or manifest.json.
• Layout aligned with the other harnesses: scripts/lib.sh (image_of honours ADAPTER_IMAGE_<adapter>), scripts/smoke.sh <adapter>, scripts/interop.sh <adapters…>, tests/cases.tsv, REQUIREMENTS.md (R1 names own/ as the one exception), compose.yaml. scripts/selftest.py stays the engine behind the two scripts; the cross-stack test now runs every client against every server. A client operation an image does not declare is unsupported, never a pass.
• Contract 1.1 (additive): upstream.independentEngine in the capability document; pysunspec2 declares true, otfabric false; results.json takes independent from it. An undeclared client operation is a usage error.
• R1 grep in ci.yml also names go-modbus and modbusctl (go-sunspec runs on go-modbus). The 11 plain "modbus" mentions under adapters/, scripts/, tests/, Makefile stay allowed.
• versions.yaml: interop_version 0.2.0, contract_version 1.1, own_implementations.otfabric, base_images.*.used_by. RELEASE.md v0.2.0 notes in this PR, so that no release PR follows.

The otfabric adapter

• Device: fixture → go-sunspec Server via go-modbus. The fixture holds raw values and go-sunspec takes engineering values, so a scaled point gets raw × 10^sf as an exact decimal (sf resolved as go-sunspec's encoder does). FC4 → exception 1 as the contract says (go-sunspec answers 2).
• Client: scan only (Discover with base addresses 40000, 0, 50000 + ReadModels). write is not declared: go-sunspec's client does not write (its LIMITATIONS.md), so client write is a usage error and the write cases are unsupported with otfabric as the client. As a device it takes pysunspec2's writes.
• print-registers equals pysunspec2's for all three fixtures except pad points (go-sunspec 0x8000, pysunspec2 0), recorded in docs/COMPATIBILITY.md; no case compares them.

Validation (local, macOS arm64)

• make ci: green (smoke pysunspec2 8/8, interop 6/6, documents valid).
• make -f own/go-sunspec/Makefile image smoke interop VERSION=dev (references built from this branch): smoke 8/8; interop 20 pass, 4 unsupported (otfabric client writes), 0 fail; documents valid.
• Same against the published v0.1.0 reference: 20 pass, 4 unsupported.

After merge: tag v0.2.0 → Release, then run Own stack (go-sunspec) from main.

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