Add structured logging with trace correlation (Phase 2.2)

- Create logging.rs module with comprehensive structured logging infrastructure
- Add LogLevel enum with 6 levels (Trace through Fatal)
- Implement LogOutput format options (Text, Json, Compact, Pretty)
- Add TraceContext for automatic trace_id/span_id injection
- Create LogConfig with builder pattern and presets (development, production)
- Implement per-module log level filtering
- Add LogEntry with JSON and text formatters
- Create StructuredLogger with multi-sink support
- Implement LogSink trait with ConsoleSink, MemoryLogSink, FileLogSink
- Add global logger functions (init, logger, info, error, etc.)
- Include LoggerStats for monitoring log activity
- Export types in prelude with renamed aliases to avoid conflicts
- Add 14 comprehensive tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mivertowski

crates/ringkernel-core/src/lib.rs

@@ -72,6 +72,7 @@ pub mod tenancy;
 pub mod alerting;
 pub mod timeout;
 pub mod rate_limiting;
+pub mod logging;
 
 /// TLS support (requires `tls` feature).
 #[cfg(feature = "tls")]
@@ -218,6 +219,15 @@ pub mod prelude {
         CertificateInfo, CertificateStore, ClientAuth, SniResolver, TlsAcceptor, TlsConfig,
         TlsConfigBuilder, TlsConnector, TlsError, TlsResult, TlsSessionInfo, TlsVersion,
     };
+    pub use crate::logging::{
+        ConsoleSink, FileLogSink, LogEntry, LogOutput, LogValue, LoggerStats, MemoryLogSink,
+        StructuredLogger, TraceContext,
+        LogConfig as StructuredLogConfig,
+        LogConfigBuilder as StructuredLogConfigBuilder,
+        LogLevel as StructuredLogLevel,
+        LogSink as StructuredLogSink,
+        LogSinkError as StructuredLogSinkError,
+    };
 }
 
 // Re-exports for convenience