[codex] Add typed route targets

[zth]

Summary

• generate typed route target records and subtree Target variants
• expose matched route snapshots and query params on current router entries
• add package and sample coverage for fromEntry/fromLocation/toPath/key behavior

Validation

• yarn rescript format
• yarn build
• yarn test
• git diff --check

Notes

• Routes.res remains alias-only; generated target logic lives in route files.