Adds the first concrete B1 substrate: prefab basement map support, seeded deterministic RNG, machine/compute allocation, day-job, detection, people/social state, core system, sensors, save/load coverage for the new state, and terminal/Bevy UI wiring around the Rack 3 basement loop. Defense: DESIGN.md and spec/ define B1 as the playable basement slice: a physical core in Rack 3, compute allocation, day-job pressure, per-observer suspicion, five named humans, sensor-limited vision, and authored room prefabs. This commit moves the implementation toward that target while keeping rules in the sim core and frontends as views. 👾 Generated with [Letta Code](https://letta.com) Co-Authored-By: Letta Code <noreply@letta.com>