Implement executable gate primitives (G1–G4) from geometry spec

[LalaSkye]

Blocked by

• Peer review: LVTECH_RUNTIME_GEOMETRY_v0.1.md invariants #21 (peer review must complete first)

Scope

Implement deterministic gate functions for G1–G4 as defined in docs/LVTECH_RUNTIME_GEOMETRY_v0.1.md.

Constraints

• Must preserve all spec invariants — no scope drift
• Each gate must be independently testable
• Fail-closed: any undefined input must reject
• Align tests to docs/LVTECH_RUNTIME_GEOMETRY_TEST_MATRIX_v0.1.md

Acceptance

• All test matrix rows pass
• CI green
• No new dependencies introduced