fix validatator name filter on missed slots

[pk910]

Show missed slots when filtering by proposer index or name

Summary

• The shouldCheckMissing gate in ChainService.GetDbBlocksByFilter was disabling reconstruction of missed slots from epoch duties whenever a ProposerIndex or ProposerName filter was set, so the filtered slots view never showed missed slots for a specific validator.
• Proposer-based filters are evaluated against epoch duty assignments and are perfectly compatible with reconstructed missing slots — the extra terms were incorrect.
• Drop filter.ProposerIndex == nil && filter.ProposerName == "" from the shouldCheckMissing condition so missed slots appear for proposer-filtered queries.

Root cause

Both terms were introduced unintentionally during a master → gloas-support merge conflict resolution in 128a7f66 ("Merge branch 'master' into gloas-support", Feb 10 2026). Two diverging tails of the shouldCheckMissing expression were concatenated and && filter.ProposerIndex == nil && filter.ProposerName == "" was tacked on, with the whole tail duplicated. The duplication was cleaned up in a later commit, but the bogus proposer terms remained.