feat: TS runtime parity — par branch labels + Promise-leak fix

[NekomyaDev]

What

TS backend parity step (roadmap v1.2): the TS runtime gains parMap / parAll / parRace helpers that wrap each lane's evaluation in its NTF v1.1 branch label — llm.call and tool.call records emitted inside a lane carry "branch": "par[i]", matching the Python runtime (#24).

• Module-level save/restore branch context (exact under JS's single-threaded sync generated code; the Python runtime needs threading.local for its worker pool)
• codegen-ts emits rt.parMap(coll, fn), rt.parAll([() => ...]), rt.parRace([() => ...])
• Latent bug fixed: par all/par race used to emit bare Promise.all([...])/Promise.race([...]) into synchronous let bindings — an un-awaited Promise leaked into the value. Thunks + a plain array return fix it.

Test

• Node 20 e2e in-sandbox: parMap/parAll/parRace all emit par[i]-tagged llm.call records; tool.call inside a lane tagged too; old traces without branch unaffected ✓
• Existing compiler e2e asserts updated to the new emission shape