Fix circular and missing module imports across L0-L2 layers:
- Add l0_transport import to QVL and PoP modules in build.zig
- Fix gateway test to use DhtService parameter
- Convert l0_transport imports to direct time imports in L1
- Fix soulkey to use module import (@import("pqxdh"))
- Fix policy.zig to use module import (@import("lwf"))
- Refactor mod.zig exports to avoid circular dependencies
- Update service.zig and utcp/socket.zig to use module imports
- Fix all QVL test files to import time directly
Results: 254+ tests passing (was 124), 1 module conflict remaining
in service tests (opq/store.zig in both lwf and opq modules).
Refs: Night Sprint 2026-02-05
Markus Maiwald
