adopt Effect.fn for service method definitions (effect-patterns.md drift) #538

Summary

docs/agents/effect-patterns.md says: prefer Effect.gen + Effect.fn("name") — do not create functions that return Effect.gen; use Effect.fn so stack traces and spans attach to the effect.

All api services currently define methods as arrow functions returning Effect.gen:

• api/src/services/nodes.ts
• api/src/services/places.ts
• api/src/services/validators.ts
• api/src/services/tenants.ts
• (+ any plugin services following the same shape)

Suggested approach

Repo-wide mechanical pass, not per-PR churn (flagged in review on #530): convert each method to Effect.fn("NodesService.list")-style definitions so traces/spans name the method. Verify the tracing/observability layering still holds with the current Effect version, and that ORPC error channels are unchanged.

Acceptance

• services use Effect.fn with span-friendly names
• effect-patterns.md example matches the real service shape
• no behavior change in route handlers / error codes