Fix MString::read() infinite retry loop, HTTPRequest parser fd leak, Log deadlock, log rotation symlink handling, and JString bounds checks

- MString::read() now gives up after repeated I/O errors instead of
  looping forever and crashing via realloc() failure (root cause of a
  recurring barant.com production crash).
- HTTPRequest::parse() no longer leaks lineParser/headerParser on a
  malformed request.
- Log gained size-based rotation (config-driven) and a non-static-mutex
  fix; a separate fix stopped rotation from destroying the logs symlink
  on its first trigger.
- File.cpp: symlink-preserving rotation support.
- JString: fixed an array-index out-of-bounds and a setString issue.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Log.h

@@ -89,8 +89,34 @@ namespace coreutils {
       
       static int seq;
 
+      ///
+      /// Rotation threshold for the static logFile, in bytes - checked
+      /// after every write that reaches it. Default 100MB. Change it
+      /// any time (takes effect on the next log call); 0 disables
+      /// rotation entirely.
+      ///
+
+      static size_t maxLogSize;
+
+      ///
+      /// How many rotated-out backups (logFile.1, logFile.2, ...) to
+      /// keep once maxLogSize is hit - the oldest beyond this count is
+      /// deleted outright, not just renamed away. Default 5.
+      ///
+
+      static int maxLogBackups;
+
     private:
-      std::mutex mtx;
+      // Static, not per-instance - every Log(level) call constructs
+      // and destructs its own temporary Log object, so a per-instance
+      // mutex (the original declaration here) provided no actual
+      // mutual exclusion between concurrent threads at all, each
+      // locking a separate mutex of their own. Only became load-bearing
+      // once rotation was added: two threads racing between "check
+      // size" and "close/rename/reopen" on the one shared logFile
+      // could otherwise write to a stale fd mid-rotation or rotate out
+      // from under an in-flight write.
+      static std::mutex mtx;
       
    };