logging

Shared logging primitives for Shiny backend services.

• SetupLogger(level, format, service, version) — configures the slog default logger (text / json / otel) and returns it.
• ContextWithLogger / LoggerFromContext — carry a logger on the context.
• NewMockLogger() — test helper for asserting log output.
• logging/middleware.RequestLogger(logger) — HTTP middleware that debug-logs request/response bodies.

Replaces the logging package (and the middleware request-logger) copied into the backend services.