Add config storage CRUD test coverage

[Zhao73]

Summary

• add CRUD regression coverage for local config storage
• cover insert, upsert versioning, list ordering, missing key behavior, deletion errors, and context cancellation/deadline paths

Closes #391

Testing

• GOPROXY=https://goproxy.cn,direct go test ./internal/storage/... -run Config

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ santoshkumarradha
❌ ChouJ

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[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 86%, aggregate ≥ 88%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.50%	87.30%	↑ +0.20 pp	🟡
sdk-go	92.10%	90.70%	↑ +1.40 pp	🟢
sdk-python	93.73%	93.63%	↑ +0.10 pp	🟢
sdk-typescript	92.80%	92.56%	↑ +0.24 pp	🟢
web-ui	89.93%	90.01%	↓ -0.08 pp	🟡
aggregate	89.03%	89.01%	↑ +0.02 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	0	—	➖ no changes
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.