feat: parse and display XEX2 main header (M1)

Implement XEX2 main header parsing with module flag decoding.
Add error handling, big-endian read utilities, CLI entry point,
and comprehensive unit + integration tests against a sample file.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/integration.rs

@@ -0,0 +1,70 @@
+use xex2tractor::header::{ModuleFlags, XEX2_MAGIC};
+
+fn sample_data() -> Vec<u8> {
+    let path = format!("{}/tests/data/default.xex", env!("CARGO_MANIFEST_DIR"));
+    std::fs::read(&path).expect("sample file should exist at tests/data/default.xex")
+}
+
+#[test]
+fn test_full_parse() {
+    let data = sample_data();
+    let xex = xex2tractor::parse(&data).unwrap();
+
+    assert_eq!(xex.header.magic, XEX2_MAGIC);
+    assert_eq!(xex.header.module_flags, ModuleFlags(0x00000001));
+    assert_eq!(xex.header.header_size, 0x00003000);
+    assert_eq!(xex.header.reserved, 0x00000000);
+    assert_eq!(xex.header.security_offset, 0x00000090);
+    assert_eq!(xex.header.header_count, 15);
+}
+
+#[test]
+fn test_parse_empty_file() {
+    let data = vec![];
+    assert!(xex2tractor::parse(&data).is_err());
+}
+
+#[test]
+fn test_parse_invalid_magic() {
+    let mut data = sample_data();
+    // Corrupt the magic bytes
+    data[0] = 0x00;
+    assert!(xex2tractor::parse(&data).is_err());
+}
+
+#[test]
+fn test_cli_runs_with_sample() {
+    let path = format!("{}/tests/data/default.xex", env!("CARGO_MANIFEST_DIR"));
+    let output = std::process::Command::new(env!("CARGO_BIN_EXE_xex2tractor"))
+        .arg(&path)
+        .output()
+        .expect("failed to run xex2tractor");
+
+    assert!(output.status.success(), "CLI should exit successfully");
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(stdout.contains("XEX2 Header"), "should display header section");
+    assert!(stdout.contains("0x58455832"), "should display magic value");
+    assert!(stdout.contains("TITLE"), "should display module flag name");
+    assert!(stdout.contains("Header Count:     15"), "should show 15 headers");
+}
+
+#[test]
+fn test_cli_no_args() {
+    let output = std::process::Command::new(env!("CARGO_BIN_EXE_xex2tractor"))
+        .output()
+        .expect("failed to run xex2tractor");
+
+    assert!(!output.status.success(), "CLI should fail without args");
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(stderr.contains("Usage"), "should print usage message");
+}
+
+#[test]
+fn test_cli_missing_file() {
+    let output = std::process::Command::new(env!("CARGO_BIN_EXE_xex2tractor"))
+        .arg("/nonexistent/file.xex")
+        .output()
+        .expect("failed to run xex2tractor");
+
+    assert!(!output.status.success(), "CLI should fail with missing file");
+}