Eliminate spdlog dependency (#773)

Removes the vendored spdlog library (~12,000 lines) and replaces it with a purpose-built logging system in zencore (~1,800 lines). The new implementation provides the same functionality with fewer abstractions, no shared_ptr overhead, and full control over the logging pipeline.

### What changed

**New logging core in zencore/logging/:**
- LogMessage, Formatter, Sink, Logger, Registry - core abstractions matching spdlog's model but simplified
- AnsiColorStdoutSink - ANSI color console output (replaces spdlog stdout_color_sink)
- MsvcSink - OutputDebugString on Windows (replaces spdlog msvc_sink)
- AsyncSink - async logging via BlockingQueue worker thread (replaces spdlog async_logger)
- NullSink, MessageOnlyFormatter - utility types
- Thread-safe timestamp caching in formatters using RwLock

**Moved to zenutil/logging/:**
- FullFormatter - full log formatting with timestamp, logger name, level, source location, multiline alignment
- JsonFormatter - structured JSON log output
- RotatingFileSink - rotating file sink with atomic size tracking

**API changes:**
- Log levels are now an enum (LogLevel) instead of int, eliminating the zen::logging::level namespace
- LoggerRef no longer wraps shared_ptr - it holds a raw pointer with the registry owning lifetime
- Logger error handler is wired through Registry and propagated to all loggers on registration
- Logger::Log() now populates ThreadId on every message

**Cleanup:**
- Deleted thirdparty/spdlog/ entirely (110+ files)
- Deleted full_test_formatter (was ~80% duplicate of FullFormatter)
- Renamed snake_case classes to PascalCase (full_formatter -> FullFormatter, json_formatter -> JsonFormatter, sentry_sink -> SentrySink)
- Removed spdlog from xmake dependency graph

### Build / test impact

- zencore no longer depends on spdlog
- zenutil and zenvfs xmake.lua updated to drop spdlog dep
- zentelemetry xmake.lua updated to drop spdlog dep
- All existing tests pass, no test changes required beyond formatter class renames

1 files changed, 6 insertions, 6 deletions

diff --git a/src/zen/progressbar.cpp b/src/zen/progressbar.cpp
index 9467ed60d..b758c061b 100644
--- a/src/zen/progressbar.cpp
+++ b/src/zen/progressbar.cpp
@@ -390,19 +390,19 @@ class ConsoleOpLogOutput : public OperationLogOutput
 {
 public:
 	ConsoleOpLogOutput(zen::ProgressBar::Mode InMode) : m_Mode(InMode) {}
-	virtual void EmitLogMessage(int LogLevel, std::string_view Format, fmt::format_args Args)
+	virtual void EmitLogMessage(const logging::LogPoint& Point, fmt::format_args Args) override
 	{
-		logging::EmitConsoleLogMessage(LogLevel, Format, Args);
+		logging::EmitConsoleLogMessage(Point, Args);
 	}
 
-	virtual void SetLogOperationName(std::string_view Name) { zen::ProgressBar::SetLogOperationName(m_Mode, Name); }
-	virtual void SetLogOperationProgress(uint32_t StepIndex, uint32_t StepCount)
+	virtual void SetLogOperationName(std::string_view Name) override { zen::ProgressBar::SetLogOperationName(m_Mode, Name); }
+	virtual void SetLogOperationProgress(uint32_t StepIndex, uint32_t StepCount) override
 	{
 		zen::ProgressBar::SetLogOperationProgress(m_Mode, StepIndex, StepCount);
 	}
-	virtual uint32_t GetProgressUpdateDelayMS() { return GetUpdateDelayMS(m_Mode); }
+	virtual uint32_t GetProgressUpdateDelayMS() override { return GetUpdateDelayMS(m_Mode); }
 
-	virtual ProgressBar* CreateProgressBar(std::string_view InSubTask) { return new ConsoleOpLogProgressBar(m_Mode, InSubTask); }
+	virtual ProgressBar* CreateProgressBar(std::string_view InSubTask) override { return new ConsoleOpLogProgressBar(m_Mode, InSubTask); }
 
 private:
 	zen::ProgressBar::Mode m_Mode;