Add professional project structure and documentation

New files:
- LICENSE (MIT) - Required legal file
- CHANGELOG.md - Version history following Keep a Changelog
- CONTRIBUTING.md - Contributor guidelines
- CODE_OF_CONDUCT.md - Community standards
- .github/ISSUE_TEMPLATE/ - Bug report and feature request forms
- .github/PULL_REQUEST_TEMPLATE.md - PR checklist
- src/stegasoo/py.typed - PEP 561 type hint marker
- examples/ - Usage examples (basic, file embedding, channel keys)

Updated:
- README.md - Added CI status badges

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

examples/basic_usage.py

@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+"""
+Basic Stegasoo Usage Example
+
+This example demonstrates how to encode and decode a secret message
+using the Stegasoo library.
+"""
+
+from pathlib import Path
+
+import stegasoo
+
+
+def main():
+    # Load your images
+    # The reference photo is your "key" - keep it secret!
+    reference_photo = Path("my_secret_photo.png").read_bytes()
+    carrier_image = Path("carrier.png").read_bytes()
+
+    # Your secret message
+    message = "This is my secret message!"
+
+    # Your credentials
+    passphrase = "correct horse battery staple"  # Use 4+ words
+    pin = "123456"  # 6-9 digits
+
+    # === ENCODE ===
+    print("Encoding message...")
+    result = stegasoo.encode(
+        message=message,
+        reference_photo=reference_photo,
+        carrier_image=carrier_image,
+        passphrase=passphrase,
+        pin=pin,
+    )
+
+    # Save the stego image
+    output_path = Path(f"secret_{result.suggested_filename}")
+    output_path.write_bytes(result.stego_image)
+    print(f"Saved to: {output_path}")
+    print(f"Capacity used: {result.capacity_used_percent:.1f}%")
+
+    # === DECODE ===
+    print("\nDecoding message...")
+    stego_image = output_path.read_bytes()
+
+    decoded = stegasoo.decode(
+        stego_image=stego_image,
+        reference_photo=reference_photo,
+        passphrase=passphrase,
+        pin=pin,
+    )
+
+    print(f"Decoded message: {decoded.message}")
+    print(f"Message type: {decoded.payload_type}")
+
+
+if __name__ == "__main__":
+    main()