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/channel_keys.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+"""
+Channel Keys Example
+
+Channel keys allow you to create private communication channels.
+Only people with the same channel key can decode messages.
+"""
+
+from pathlib import Path
+
+import stegasoo
+from stegasoo.channel import generate_channel_key, get_channel_fingerprint
+
+
+def main():
+    # Generate a channel key for your group
+    channel_key = generate_channel_key()
+    fingerprint = get_channel_fingerprint(channel_key)
+
+    print("=== Channel Key Generated ===")
+    print(f"Key: {channel_key}")
+    print(f"Fingerprint: {fingerprint}")
+    print("\nShare this key securely with your group members!")
+    print("-" * 40)
+
+    # Load images
+    reference_photo = Path("my_secret_photo.png").read_bytes()
+    carrier_image = Path("carrier.png").read_bytes()
+
+    # Encode with channel key
+    print("\nEncoding message with channel key...")
+    result = stegasoo.encode(
+        message="Secret group message!",
+        reference_photo=reference_photo,
+        carrier_image=carrier_image,
+        passphrase="correct horse battery staple",
+        pin="123456",
+        channel_key=channel_key,  # Add the channel key
+    )
+
+    stego_data = result.stego_image
+    print(f"Encoded successfully!")
+
+    # Decode with correct channel key
+    print("\nDecoding with correct channel key...")
+    decoded = stegasoo.decode(
+        stego_image=stego_data,
+        reference_photo=reference_photo,
+        passphrase="correct horse battery staple",
+        pin="123456",
+        channel_key=channel_key,  # Same channel key
+    )
+    print(f"Message: {decoded.message}")
+
+    # Try to decode with wrong channel key
+    print("\nTrying to decode with wrong channel key...")
+    wrong_key = generate_channel_key()
+    try:
+        stegasoo.decode(
+            stego_image=stego_data,
+            reference_photo=reference_photo,
+            passphrase="correct horse battery staple",
+            pin="123456",
+            channel_key=wrong_key,  # Different channel key
+        )
+        print("ERROR: Should have failed!")
+    except (stegasoo.DecryptionError, stegasoo.ExtractionError):
+        print("Correctly rejected - wrong channel key!")
+
+
+if __name__ == "__main__":
+    main()