Function action_gate 

pub fn action_gate(dimensions: &[GateDimension]) -> GateResult

Evaluate an action through a multi-dimension policy gate.

The gate logic (inspired by AI safety frameworks):

1. Check all hard_block dimensions first. Any -1 → immediate Block.
2. Compute weighted aggregate of all dimensions.
3. Map aggregate to ternary: +1 = Proceed, 0 = Hold, -1 = Block.