feat(bifrost): skip XMR monovault keygen network-wide

What

Network-wide skip of the XMR/FROST monovault keygen in the bifrost signer (processKeygenBlock), so the churn can resume without re-triggering the 95-party sidecar-DKG mass-jailing.

Why

The full-active-set (~95-party) XMR monovault FROST keygen fails at scale and mass-jails members — via judgeLateSigner on a retry-round success (the ~79/95 jailing). HALTCHURNING has been held network-wide purely to suppress this keygen, which blocks the churn entirely.

A keygen with zero MsgTssPool reports reaches no consensus, so no jail/slash fires (x/thorchain/handler_tss.go). No XMR monovault exists on mainnet, so skipping strands no funds. This lets the churn resume without a consensus release (unlike the HaltMonovaultKeygen mimir, !4919 — the cleaner permanent version, worth landing after).

Change

bifrost/signer/sign.go — at the top of the processKeygenBlock loop, continue past KeygenType_XMRMonovaultKeygen. Single point; covers initial dispatch and the retry path, before the Monero sidecar DKG is entered.

Deploy / rollout

⚠️ Deploy to ALL active + ready nodes before churn resumes. Partial coverage (<1/3 of members) can let the failure-blame path jail the patched members. >1/3 patched → nobody jailable; ~all (incl ready nodes about to churn in) → clean.

Sequence: kpg6ac LTC drained ✅ → deploy this to all nodes → lift HALTCHURNING.

Remove once the FROST keygen reliability fix or !4919 lands.