fix(dev): include layout component deps in incremental builds

[cssbruno]

Summary

• Include component references from each page's resolved layout chain when building the dev incremental reverse component index.
• Keep component file assets in incremental buildgen output and asset manifests by planning component file assets alongside scoped JS/runtime assets.
• Add regressions for layout-only component changes and component asset metadata/file emission through incremental builds.

Review Feedback

Addresses Codex review comments:

• Rebuild pages for layout-only component dependencies.
• Keep component file assets in component incremental rebuilds.

Verification

• go test ./cmd/gowdk ./internal/buildgen
• go test ./internal/buildgen ./internal/appgen ./internal/compiler
• go build ./cmd/gowdk
• go run ./cmd/gowdk build --out /tmp/gowdk-incremental-review-build examples/pages/*.gwdk
• go test ./...

LLM Assistance

• Implemented by Codex from automated review feedback.