config: detect recursive includes

[officialasishkumar]

Summary

• track canonicalized config file paths while processing deprecated include chains
• return a clear recursive include error instead of recursing indefinitely
• add coverage for self-includes and two-file include cycles

Fixes #1627

Test plan

• go test ./pkg/build/types
• go test ./pkg/build/... ./internal/cli
• go test ./...
• git diff --check
• go mod tidy && git diff --exit-code -- go.mod go.sum

[coreydaley-cg]

The fix is right and everything is green except commit signing, which blocks the merge button. Can you sign the commit and force-push? If that's a hassle, say so and a maintainer can re-land it with you as co-author.