[S3-007] Reconcile the Roman barracks construction cost between the manual and the reference definition

Problem

The pinned manual's building-material table (building.htm, SHA-256 10dcbad8d7c02a7873b263f1db81e7561368467f429c4b6b6113758122d65a9e) lists the Roman barracks at 4 wood (planks) and 5 stone. The pinned reference remake's barrack.xml (6ad8c42) requires 5 planks and 4 stone.

For every other Roman building the engine defines, the reference construction totals match the manual (checked by generating resources/game/engine/reference-geometry.ts), so this is the one disagreement found.

Acceptance criteria

• Observe the barracks cost in an identified original build (S3-002) for each edition profile that has the building.
• Record the result as O evidence and select the value per rules profile (S3-007); keep both documentary sources in the ledger.
• Add the barracks to the Roman rules profile with that evidence before S3-051 relies on it.

Context

Found while adopting reference geometry in da2a104. The barracks is not yet in the engine's Roman profile, so nothing currently depends on either value. Blocked by S3-002 for the observation.

S3-051 now relies on the barracks (36af2f0). The rules profile 0.3.0 uses the manual candidate (4 planks, 5 stone) and records the reference value in a U evidence entry, buildings.barracks.cost-discrepancy, owned by S3-007. The cost still needs the original observation before this can close.