feat: add CLI interface with command parsing and tests

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

test_cli.c

@@ -0,0 +1,58 @@
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+#include "engine.h"
+#include "cli.h"
+
+// Minimal test: just ensure parsing doesn't crash
+static void test_cli_parse(void) {
+    printf("Test CLI parse... ");
+    
+    // Create a minimal engine (no JACK needed for parsing)
+    Engine engine;
+    memset(&engine, 0, sizeof(engine));
+    engine.sample_rate = 48000;
+    engine.control_channel = 0;
+    engine.quantize_mode = QUANTIZE_OFF;
+    engine.quantize_threshold = 0;
+    engine.queued_triggers = NULL;
+    engine.transport.rolling = false;
+    engine.transport.clock_count = 0;
+    engine.transport.beat_position = 0;
+    engine.transport.bar_position = 0;
+    engine.transport.sample_position = 0;
+    for (int i = 0; i < MAX_CLIPS; i++) {
+        engine.clips[i].state = CLIP_EMPTY;
+        engine.clips[i].buffer = NULL; // not needed for parsing
+        engine.clips[i].buffer_size = 0;
+        engine.clips[i].write_position = 0;
+        engine.clips[i].read_position = 0;
+    }
+    
+    // Test valid commands
+    assert(cli_process_line(&engine, "help") == 1);
+    assert(cli_process_line(&engine, "trigger clip 0") == 1);
+    assert(cli_process_line(&engine, "trigger scene 1") == 1);
+    assert(cli_process_line(&engine, "reset clip 2") == 1);
+    assert(cli_process_line(&engine, "reset transport") == 1);
+    assert(cli_process_line(&engine, "quantize beat") == 1);
+    assert(cli_process_line(&engine, "threshold 1000") == 1);
+    assert(cli_process_line(&engine, "quit") == 0);
+    
+    // Test invalid commands (should not crash)
+    assert(cli_process_line(&engine, "") == 1);
+    assert(cli_process_line(&engine, "unknown") == 1);
+    assert(cli_process_line(&engine, "trigger") == 1);
+    assert(cli_process_line(&engine, "reset") == 1);
+    assert(cli_process_line(&engine, "quantize") == 1);
+    assert(cli_process_line(&engine, "threshold") == 1);
+    
+    printf("PASSED\n");
+}
+
+int main(void) {
+    printf("Running CLI tests...\n\n");
+    test_cli_parse();
+    printf("\nAll CLI tests passed!\n");
+    return 0;
+}