api: GET /api/v1/transmission-lines endpoints

[victorquinn]

Summary

Implement read API endpoints for transmission lines: list with filtering/pagination, detail by ID.

Files to Create

• app/api/v1/transmission-lines/route.ts — List endpoint
• app/api/v1/transmission-lines/[id]/route.ts — Detail endpoint

Query Parameters (List)

• voltageClass — Filter by voltage class
• owner — Filter by owner (trigram search)
• status — Filter by status
• minVoltage, maxVoltage — Voltage range filter
• fields, sort, order, cursor, limit — Standard pagination

Note

Transmission line geometry is handled via PMTiles (existing tile pipeline), not the API. API serves metadata only.

Acceptance Criteria

• List with filtering and pagination
• Detail by ID
• Owner trigram search working
• npm run build passes

Spec ref: Section 4.4
Blocked by: #5, #7 (API utilities, seed)
Blocks: Transmission lines page migration