revert(covgate): remove build-cache pre-warm (#34–#36)

[ben-miru]

What

Reverts the covgate build-cache pre-warm feature in its entirety. covgate no longer pre-warms the Go build cache before its parallel coverage runs.

Reverts, in order (newest first):

• perf(covgate): instrument the build-cache pre-warm #36 perf(covgate): instrument the build-cache pre-warm (794e725)
• feat(covgate): report build-cache pre-warm duration #35 feat(covgate): report build-cache pre-warm duration (6a0cc47)
• perf(covgate): pre-warm build cache before parallel coverage runs #34 perf(covgate): pre-warm build cache before parallel coverage runs (0c3c0af)

Why

We no longer want covgate to pre-warm the build cache. The pre-warm compiled an extra artifact set that inflated the CI gobuild-test cache and pushed the backend repo back over the 10 GB Actions cache quota (the very regression #36 tried to walk back). Rather than keep iterating on the pre-warm, we're removing it.

How

Three git revert commits, preserving history/attribution. The reverted internal/services/covgate/ and internal/services/gocover/ files are byte-identical to their pre-feature state, and the feature's design doc (plans/completed/20260624-covgate-prewarm-build-cache.md) is removed.

Validation

• No lingering prewarm / PrewarmBuild references anywhere in internal/, cmd/, or scripts/.
• Full scripts/preflight.sh passes clean: covgate coverage 94.3% across all 30 packages, gocover 92.6% (≥ 92.1% required), custom lint + gofumpt + golangci-lint + deadcode + surface-lint all green.
• Clean revert with no conflicts against current main; unrelated later commits (ci: migrate CI runners to Blacksmith #37 CI, chore(deps): bump go dependencies via update-deps script #38 dep bumps, chore(lint): raise default max-param-count from 5 to 6 #39 max-param-count) required no adjustment.

🤖 Generated with Claude Code

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