Standardize error handling patterns and improve ErrorHandler integration.

- Added a comprehensive error propagation standardization report detailing dominant patterns, inconsistencies, and recommended remediations (`docs/audits/error-propagation-standardization.md`).
- Integrated `ErrorHandler` into key components, including `main.cc` for robust exception reporting, and added centralized logging to a user state path.
- Introduced EINTR-safe syscall wrappers (`SyscallWrappers.h`, `.cc`) to improve resilience of file and metadata operations.
- Enhanced `DEVELOPER_GUIDE.md` with an error handling conventions section, covering pattern guidelines and best practices.
- Identified gaps in `PieceTable` and internal helpers; deferred fixes with detailed recommendations for improved memory allocation error reporting.

CMakeLists.txt

@@ -142,6 +142,8 @@ set(COMMON_SOURCES
         HelpText.cc
         KKeymap.cc
         Swap.cc
+        ErrorHandler.cc
+        SyscallWrappers.cc
         TerminalInputHandler.cc
         TerminalRenderer.cc
         TerminalFrontend.cc
@@ -337,6 +339,8 @@ if (BUILD_TESTS)
             Command.cc
             HelpText.cc
             Swap.cc
+            ErrorHandler.cc
+            SyscallWrappers.cc
             KKeymap.cc
             SwapRecorder.h
             OptimizedSearch.cc