[Refactor]: Hide row-position internals behind safer mapping

[AashishH15]

Problem

Row mappers use numeric indices, coupling object construction to SQL select order.

Evidence

• Row mappers depend on numeric column positions, for example vault_from_row (line 78) and node_from_row (line 96).

Scope & constraints

No response

Proposed approach

• Define canonical SELECT lists as constants per entity and keep mapping adjacent. Optionally add named-column helper accessors.
• group select lists as constants per entity or use named-column helpers to reduce accidental mapping drift.

Acceptance criteria

• Reduced chance of mapping drift when SELECT changes.
• Clear contract between query and mapper.

Test plan

• Run existing unit/integration tests; add targeted mapping test if needed.