fix(graphql): support msgscan legacy filters

[fewensa]

Summary

• add msgscan-compatible GraphQL input/order type aliases
• add legacy totalCount connection fields used by msgscan stats queries
• map msgscan legacy filters to SQL where clauses

Tests

• cargo fmt
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --locked
• cargo test --no-default-features --test graphql_server test_graphql_schema_exposes_pages_without_connections -- --nocapture