feat: add PE verification and complete extraction pipeline (M6)

Add PE header verification (MZ signature, PE signature, POWERPCBE
machine type) to the extraction pipeline. Implement master key trial
with validation for encrypted files. Update CLI extract command to
show encryption/compression info. Update README with extract usage.

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

README.md

@@ -4,11 +4,15 @@ A tool for extracting and inspecting Xbox 360 XEX2 executable files, written in
 
 ## Usage
 
+### Inspect
+
+Display XEX2 file information (headers, security info, etc.):
+
 ```sh
-xex2tractor <file.xex>
+xex2tractor inspect <file.xex>
 ```
 
-### Example Output
+#### Example Output
 
 ```
 === XEX2 Header ===
@@ -35,16 +39,9 @@ Header Count:     15
 [FILE_FORMAT_INFO]
   Encryption:  Normal (AES-128-CBC)
   Compression: Normal (LZX)
-
-[STATIC_LIBRARIES] (12 libraries)
-  XAPILIB  2.0.3215.0 (Unknown(64))
-  D3D9     2.0.3215.1 (Unknown(64))
+  Window Size: 0x8000 (32 KB)
   ...
 
-[IMPORT_LIBRARIES] (2 libraries)
-  xam.xex v2.0.4552.0 (min v2.0.4552.0) - 104 imports
-  xboxkrnl.exe v2.0.4552.0 (min v2.0.4552.0) - 294 imports
-
 === Security Info ===
 Header Size:          0x00000F34 (3892 bytes)
 Image Size:           0x00920000 (9568256 bytes)
@@ -54,12 +51,32 @@ Load Address:         0x82000000
 Region:               0xFFFFFFFF [ALL REGIONS]
 Allowed Media Types:  0x00000004 [DVD_CD]
 ...
-
-Page Descriptors (146 entries, 64KB pages):
-  #0    Unknown(0) 19   pages  ( 1245184 bytes)  offset +0x00000000  SHA1: B136058FBBAD...
-  ...
 ```
 
+### Extract
+
+Extract the decrypted and decompressed PE image from a XEX2 file:
+
+```sh
+xex2tractor extract <file.xex> [output.exe]
+```
+
+If no output path is given, defaults to the input filename with `.exe` extension.
+
+#### Example
+
+```sh
+$ xex2tractor extract default.xex default.exe
+Encryption:  Normal (AES-128-CBC)
+Compression: Normal (LZX)
+Extracted PE image (9568256 bytes) -> default.exe
+```
+
+Supports:
+- AES-128-CBC decryption (retail, devkit, and XEX1 master keys)
+- No compression, basic (zero-fill), and normal (LZX) decompression
+- PE header verification (MZ signature, PE signature, POWERPCBE machine type)
+
 ## Building
 
 ```sh