test(functional): fix Docker-backed SDK test infra

[santoshkumarradha]

Fixes #713

Summary

Fixes the Docker-backed SDK functional test infrastructure and makes the new tests exercise real end-to-end behavior.

Infrastructure fixes

• Use the repository root as the Docker build context so deployments/docker/Dockerfile.control-plane can copy control-plane/... paths.
• Poll the actual control-plane health route at /api/v1/health in Docker healthchecks and wait scripts.
• Use supported control-plane env vars for postgres mode: AGENTFIELD_STORAGE_MODE=postgres and AGENTFIELD_POSTGRES_URL.
• Add host.docker.internal host mapping so the containerized control plane can call agents running on the host during functional tests.

SDK functional test fixes

• Update Python functional tests to use the current SDK API: Agent(..., agentfield_server=...).
• Pass the Agent instance itself to uvicorn instead of agent.app.
• Start Python test agents on 0.0.0.0 while probing localhost for readiness.
• Avoid empty execute payloads rejected by the control plane.
• Add Go SDK skill registration support and include skills in control-plane node registration.
• Make Go agent startup bind its listener before registration so callback validation is not racy.
• Update Go functional execution coverage to actually call /api/v1/execute/test-go-execution.add and assert sum == 5.

Verification

• docker compose -f test-infra/docker-compose.yml config
• ./test-infra/scripts/start-env.sh
• cd sdk/python && /tmp/agentfield-py-functional-venv/bin/pytest --collect-only -m functional tests/functional
• cd sdk/python && /tmp/agentfield-py-functional-venv/bin/pytest -m functional tests/functional/test_agent_registration.py -q
• cd sdk/go && go test ./agent
• cd sdk/go && go test -tags functional -run TestFunctionalExecution -count=1 -v .

[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Python	9.4 KB	+4%	0.31 µs	-11%	✓	✓
Go	240 B	-14%	0.72 µs	-28%	✓	✓

✓ No regressions detected

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 84%, aggregate ≥ 85%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.00%	87.40%	↓ -0.40 pp	🟡
sdk-go	91.90%	92.00%	↓ -0.10 pp	🟢
sdk-python	93.76%	93.73%	↑ +0.03 pp	🟢
sdk-typescript	90.05%	90.42%	↓ -0.37 pp	🟢
web-ui	84.82%	84.79%	↑ +0.03 pp	🟡
aggregate	85.62%	85.75%	↓ -0.13 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	0	—	➖ no changes
sdk-go	107	95.00%	✅
sdk-python	0	—	➖ no changes
sdk-typescript	0	—	➖ no changes
web-ui	0	—	➖ no changes

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.