feat(pcb_component): add relational_constraints for hierarchical auto-placement

[billwestrup]

Summary

Adds an optional relational_constraints field to pcb_component to express soft proximity relationships between components. This is useful for hierarchical and tile-based auto-placement pipelines.

Motivation

When building auto-placement engines for dense mixed-signal boards (e.g. RTLS trackers with nRF9151, nPM1300, nRF5340, BQ51013B co-located on a 50×82mm 2-layer PCB), you need a way to encode "this decoupling cap must stay within 8mm of its IC" without hard-coding absolute XY coordinates.

The existing position_mode / anchor_position / anchor_alignment fields cover deterministic relative placement (component A at exact offset from component B). relational_constraints covers the complementary soft constraint case — telling a physics-based or greedy placement engine what the goal is, while letting the engine decide the exact position.

Fields Added

relational_constraints?: {
  // Name of the target component to stay near (soft constraint)
  anchor_to?: string
  // Maximum allowed Euclidean distance in mm between centers
  max_distance?: number
  // Grouping hint for tile/cluster assignment
  keep_near?: string
}

All fields are optional. The constraints are advisory — they are intended to be consumed by placement engines, not enforced by Zod validation.

Example Usage

{
  "type": "pcb_component",
  "pcb_component_id": "pcb_component_C_DEC2",
  "source_component_id": "...",
  "center": { "x": -18.3, "y": -28.1 },
  "width": 1.6, "height": 0.8,
  "layer": "top", "rotation": 0,
  "obstructs_within_bounds": true,
  "relational_constraints": {
    "anchor_to": "U1_NRF9151",
    "max_distance": 8,
    "keep_near": "T1_RF"
  }
}

Changes

• src/pcb/pcb_component.ts: adds relational_constraints to both the Zod schema and the PcbComponent TypeScript interface
• Build and expectTypesMatch pass cleanly (tsc --noEmit exit 0)

Testing

The expectTypesMatch<PcbComponent, InferredPcbComponent>(true) structural check at the bottom of the file ensures the interface and Zod-inferred type stay in sync — this already validates the new field.