Populate WorldStateView.players in ClusterManager

[rebelmachina]

Epic: #64 (AffinityEngine)
Depends on: #72 (SpatialIndex snapshot_entities)

What

Modify ClusterManager::run_evaluation_cycle() in crates/arcane-infra/src/cluster_manager.rs to populate WorldStateView.players and ClusterInfo.player_ids from the spatial index.

Current state (lines 87-92)

let view = WorldStateView {
    timestamp: 0.0,
    evaluation_budget_ms: 50,
    clusters,
    players: vec![],    // ← always empty
};

After

• Call self.spatial_index.snapshot_entities() to get entity data
• Build PlayerInfo for each entity (position via X/Z mapping, velocity=0, guild/party=None)
• Populate ClusterInfo.player_ids per cluster
• Pass populated players to WorldStateView

Notes

• velocity will be Vec2::new(0.0, 0.0) — SpatialIndex doesn't track velocity
• guild_id and party_id will be None — requires SpacetimeDB integration (not in scope)
• X/Z position mapping matches existing centroid mapping on line 82
• RulesEngine ignores players field, so this is backward-compatible

Acceptance criteria

• WorldStateView.players is populated with entity data
• ClusterInfo.player_ids is populated per cluster
• cargo test --workspace passes
• RulesEngine behavior is unchanged

Spec

See arcane-engine repo: in_08_00_integration_report.md §2.5

[rebelmachina]

Implemented in PR #77. run_evaluation_cycle() in cluster_manager.rs now calls snapshot_entities(), builds a cluster_player_ids map, and populates WorldStateView.players with full PlayerInfo entries (position from X/Z, velocity zero, guild_id/party_id None). Previously players was always vec![].