Guard emergency recovery ViewID transitions

[Frozen]

Dev counterpart of #5107.

Summary

• activate a one-off 1,000,000,000 ViewID floor for mainnet shard 0 at retained height 92,730,034 and shard 1 at retained height 94,978,278
• install the floor before networked consensus signing and derive the leader deterministically from the recovery view
• validate ANNOUNCE blocks synchronously before PREPARE, bind message and block ViewIDs, and reject unsafe COMMITTED or carried prepared blocks
• accept NEWVIEW only from the deterministically selected leader
• keep ViewID state monotonic while the floor is active and use checked arithmetic for view advancement and leader gaps

This extracts only the ViewID/view-change protection from Frozen#13. It does not include abandoned-block rejection, rollback, staged-sync, receipt, staking, or recovery feature-freeze changes.

Test

• go test -mod=readonly -count=1 ./consensus ./cmd/harmony
• go vet -mod=readonly ./consensus ./cmd/harmony
• go test -race -mod=readonly -count=1 ./consensus -run 'Test(EmergencyRecovery|Recovery|NewViewRequires)'
• git diff --check

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