[codex] Add navigable Ghost context entrypoints

[nahiyankhan]

Summary

• Derive a runtime fingerprint graph for Ghost context selection.
• Emit compact, path-aware context entrypoints instead of pasting the full fingerprint into prompt.md.
• Use the same selected context flow in ghost review markdown while preserving JSON compatibility.

Validation

• pnpm test
• pnpm check
• pnpm build
• Pre-push hook reran pnpm build, pnpm check, and pnpm test successfully.

Notes

Local sandbox and real-agent harness files used for manual testing are intentionally ignored locally and are not part of this PR.