feat: add cJSON and SQLite amalgamation source files under deps/

Add the cJSON library (cJSON.c, cJSON.h) and SQLite amalgamation
(sqlite3.c, sqlite3.h, sqlite3ext.h, shell.c) as vendored dependencies
in the deps/ directory for use by the project build system.

example/signal_demo.wren

@@ -0,0 +1,39 @@
+// retoor <retoor@molodetz.nl>
+
+import "signal" for Signal
+
+System.print("=== Signal Module Demo ===\n")
+
+System.print("--- Available Signal Constants ---")
+System.print("SIGHUP:  %(Signal.SIGHUP)")
+System.print("SIGINT:  %(Signal.SIGINT)")
+System.print("SIGQUIT: %(Signal.SIGQUIT)")
+System.print("SIGTERM: %(Signal.SIGTERM)")
+System.print("SIGUSR1: %(Signal.SIGUSR1)")
+System.print("SIGUSR2: %(Signal.SIGUSR2)")
+
+System.print("\n--- Signal API Overview ---")
+System.print("The Signal module provides:")
+System.print("  Signal.trap(signum, fn)  - Set a handler for a signal")
+System.print("  Signal.ignore(signum)    - Ignore a signal")
+System.print("  Signal.reset(signum)     - Reset to default behavior")
+
+System.print("\n--- Example Usage ---")
+System.print("To handle SIGINT (Ctrl+C):")
+System.print("  Signal.trap(Signal.SIGINT) {")
+System.print("    System.print(\"Interrupted!\")")
+System.print("  }")
+
+System.print("\nTo ignore SIGTERM:")
+System.print("  Signal.ignore(Signal.SIGTERM)")
+
+System.print("\nTo reset SIGHUP to default:")
+System.print("  Signal.reset(Signal.SIGHUP)")
+
+System.print("\n--- Notes ---")
+System.print("Signal handling is useful for:")
+System.print("  - Graceful shutdown on SIGTERM/SIGINT")
+System.print("  - Reloading configuration on SIGHUP")
+System.print("  - Custom actions on SIGUSR1/SIGUSR2")
+
+System.print("\n--- Demo Complete ---")