Add import, forget, and drift to plan summaries

[emmanuelmaduwuba-lyft]

Summary

Brings the neptune plan summary in line with upstream Atlantis's PlanSuccess.Summary():

• Import and forget counts in the one line summary, using the same wording as the Terraform CLI (Plan: 1 to import, 0 to add, 1 to change, 0 to destroy, 1 to forget.).
• Drift note in the check run's Plan Summary section when resources changed outside of Terraform (**Note: 2 resources have changed outside of Terraform.**), read from the plan JSON's resource_drift instead of matching log text.

Dependency bump

Change.Importing and Plan.ResourceDrift need hashicorp/terraform-json >= v0.17. This bumps it from v0.14.0 to v0.22.1, the newest release that doesn't also raise hashicorp/go-version (used in ~40 files). The only other go.mod changes are indirect deps with no direct importers here (go-cty, go-cmp, go-textseg). terraform-json itself is only imported by summary.go.

The forget action constant (tfjson.ActionForget) only exists in v0.23+, so it's defined locally rather than taking the go-version bump.

Behavior notes

• PlanSummary.IsEmpty() is intentionally unchanged (creates/updates/deletes only), since the plan review gate depends on it. Display uses a separate check, so import- or forget-only plans no longer show "No plan summary created".
• Drift is informational and never counted as a planned change.
• New fields on PlanSummary are additive, so existing workflow histories and payloads decode with zero values.

Test plan

• New unit tests for import, forget, import+forget, drift, and the drift note (summary_test.go)
• New renderer tests for the check-run template with and without drift (renderer_test.go, first tests for this package)
• go build ./..., go vet, gofmt clean
• go test ./...: all packages pass except server/neptune/workflows TestDeployWorkflow, which hits its 3s Temporal test-env timeout under full parallel load. It fails the same way on main and passes in isolation with and without this change.