api: GET /api/v1/pricing-nodes endpoints

[victorquinn]

Summary

Implement read API endpoints for pricing nodes: list with filtering/pagination/search, detail by slug, version history.

Files to Create

• app/api/v1/pricing-nodes/route.ts — List endpoint
• app/api/v1/pricing-nodes/[slug]/route.ts — Detail endpoint
• app/api/v1/pricing-nodes/[slug]/versions/route.ts — Version history

Query Parameters (List)

• search — Full-text + trigram search
• iso — Filter by ISO (CAISO, PJM, etc.)
• nodeType — Filter by node type
• state — Filter by state
• zone — Filter by zone
• lat, lng, radius — Spatial nearest-neighbor
• fields — Sparse field projection
• sort, order, cursor, limit — Pagination

Acceptance Criteria

• List endpoint with all filters working
• Cursor-based pagination
• Detail by slug returns full entity
• Version history endpoint
• Spatial queries (nearest-neighbor) working
• Zod validation on all inputs
• Proper error responses
• npm run build passes

Spec ref: Sections 4.3–4.5
Blocked by: #5, #7 (API utilities, seed)
Blocks: Pricing nodes page migration