fix(dataflow): attach non-CFG graph selections

[MikeeI]

Summary

Keep internal CFG node identity available when callers select only PDG, DFG, or SDG output.
Apply graph selectors at the public attachment boundary.

Evidence

• applyDataflow currently skips every function whose selected IR omits cfg.
• A successful SDG-only run consequently emits no SDG data in the wire tree.

Changes

• Separate internal attachment substrate from visible graph fields.
• Preserve existing selector and schema behavior.

Risks and boundaries

• Unselected CFG edges remain absent from public output.
• Graph computation algorithms remain unchanged.

Verification

• bun test test/dataflow.test.ts
• bun test
• bun run typecheck

I checked the relevant issues, comments, pull requests, and discussions; this pull request is not a duplicate.

Disclosure

Investigated thoroughly with GPT-5.6 at extra-high reasoning effort.
I used Oh My Pi as the agent framework.
This report is not generic or unreviewed AI-generated output.
Its claims were checked against the cited evidence.
It includes the relevant detail intended to help maintainers resolve the issue.
If reports like this are not useful to the project, please let me know.
I will refrain from submitting similar reports.
My intent is to help without wasting maintainer time or energy or discouraging their work.
Thank you for your work.