/rpc/v2 tipset selectors (latest / finalized / safe) parity

[Reiers]

What

Lotus (and its gateway) are converging on the v2 RPC surface built around TipSetSelector tags: latest, finalized, safe, plus height/key anchors. Serve the same selector semantics from Lantern.

Why

• Ecosystem tooling will increasingly speak /rpc/v2; parity keeps "real Curio/lotus binaries bind transparently" true over time.
• Lantern can serve these selectors more honestly than a gateway: our finalized is BLS-verified F3 (and, after the FRC-0089 lift, max(ecfinality, F3) exactly like lotus semantics: finalized = max(ec-finalized, f3-finalized), safe = max(finalized, head - SafeHeightDistance)).

Depends on

• FRC-0089 calculator lift (Lift FRC-0089 EC finality calculator (lotus chain/ecfinality): observed-data finality without F3 #96) for the ec-finalized half of the semantics.

Acceptance

• Selector resolution helper (tag -> tipset) shared by RPC methods
• finalized/safe semantics match lotus chain_v2
• Covered on the compat test against a live lotus binding

Low priority until a consumer actually asks for v2; filed so the parity gap is tracked.