feat(multi-llm): Phase 1 - Foundation adaptor architecture

Implement base adaptor pattern for multi-LLM support (Issue #179)

**Architecture:**
- Created adaptors/ package with base SkillAdaptor class
- Implemented factory pattern with get_adaptor() registry
- Refactored Claude-specific code into ClaudeAdaptor

**Changes:**
- New: src/skill_seekers/cli/adaptors/base.py (SkillAdaptor + SkillMetadata)
- New: src/skill_seekers/cli/adaptors/__init__.py (registry + factory)
- New: src/skill_seekers/cli/adaptors/claude.py (refactored upload + enhance logic)
- Modified: package_skill.py (added --target flag, uses adaptor.package())
- Modified: upload_skill.py (added --target flag, uses adaptor.upload())
- Modified: enhance_skill.py (added --target flag, uses adaptor.enhance())

**Tests:**
- New: tests/test_adaptors/test_base.py (10 tests passing)
- All existing tests still pass (backward compatible)

**Backward Compatibility:**
- Default --target=claude maintains existing behavior
- All CLI tools work exactly as before without --target flag
- No breaking changes

**Next:** Phase 2 - Implement Gemini, OpenAI, Markdown adaptors

src/skill_seekers/cli/enhance_skill.py

@@ -1,12 +1,18 @@
 #!/usr/bin/env python3
 """
 SKILL.md Enhancement Script
-Uses Claude API to improve SKILL.md by analyzing reference documentation.
+Uses platform AI APIs to improve SKILL.md by analyzing reference documentation.
 
 Usage:
-    skill-seekers enhance output/steam-inventory/
+    # Claude (default)
     skill-seekers enhance output/react/
-    skill-seekers enhance output/godot/ --api-key YOUR_API_KEY
+    skill-seekers enhance output/react/ --api-key sk-ant-...
+
+    # Gemini
+    skill-seekers enhance output/react/ --target gemini --api-key AIzaSy...
+
+    # OpenAI
+    skill-seekers enhance output/react/ --target openai --api-key sk-proj-...
 """
 
 import os
@@ -195,18 +201,26 @@ Return ONLY the complete SKILL.md content, starting with the frontmatter (---).
 
 def main():
     parser = argparse.ArgumentParser(
-        description='Enhance SKILL.md using Claude API',
+        description='Enhance SKILL.md using platform AI APIs',
         formatter_class=argparse.RawDescriptionHelpFormatter,
         epilog="""
 Examples:
-  # Using ANTHROPIC_API_KEY environment variable
+  # Claude (default)
   export ANTHROPIC_API_KEY=sk-ant-...
-  skill-seekers enhance output/steam-inventory/
+  skill-seekers enhance output/react/
 
-  # Providing API key directly
+  # Gemini
+  export GOOGLE_API_KEY=AIzaSy...
+  skill-seekers enhance output/react/ --target gemini
+
+  # OpenAI
+  export OPENAI_API_KEY=sk-proj-...
+  skill-seekers enhance output/react/ --target openai
+
+  # With explicit API key
   skill-seekers enhance output/react/ --api-key sk-ant-...
 
-  # Show what would be done (dry run)
+  # Dry run
   skill-seekers enhance output/godot/ --dry-run
 """
     )
@@ -214,7 +228,11 @@ Examples:
     parser.add_argument('skill_dir', type=str,
                        help='Path to skill directory (e.g., output/steam-inventory/)')
     parser.add_argument('--api-key', type=str,
-                       help='Anthropic API key (or set ANTHROPIC_API_KEY env var)')
+                       help='Platform API key (or set environment variable)')
+    parser.add_argument('--target',
+                       choices=['claude', 'gemini', 'openai'],
+                       default='claude',
+                       help='Target LLM platform (default: claude)')
     parser.add_argument('--dry-run', action='store_true',
                        help='Show what would be done without calling API')
 
@@ -249,18 +267,57 @@ Examples:
         print(f"  skill-seekers enhance {skill_dir}")
         return
 
-    # Create enhancer and run
+    # Check if platform supports enhancement
     try:
-        enhancer = SkillEnhancer(skill_dir, api_key=args.api_key)
-        success = enhancer.run()
+        from skill_seekers.cli.adaptors import get_adaptor
+
+        adaptor = get_adaptor(args.target)
+
+        if not adaptor.supports_enhancement():
+            print(f"❌ Error: {adaptor.PLATFORM_NAME} does not support AI enhancement")
+            print(f"\nSupported platforms for enhancement:")
+            print("  - Claude AI (Anthropic)")
+            print("  - Google Gemini")
+            print("  - OpenAI ChatGPT")
+            sys.exit(1)
+
+        # Get API key
+        api_key = args.api_key
+        if not api_key:
+            api_key = os.environ.get(adaptor.get_env_var_name(), '').strip()
+
+        if not api_key:
+            print(f"❌ Error: {adaptor.get_env_var_name()} not set")
+            print(f"\nSet your API key for {adaptor.PLATFORM_NAME}:")
+            print(f"  export {adaptor.get_env_var_name()}=...")
+            print("Or provide it directly:")
+            print(f"  skill-seekers enhance {skill_dir} --target {args.target} --api-key ...")
+            sys.exit(1)
+
+        # Run enhancement using adaptor
+        print(f"\n{'='*60}")
+        print(f"ENHANCING SKILL: {skill_dir}")
+        print(f"Platform: {adaptor.PLATFORM_NAME}")
+        print(f"{'='*60}\n")
+
+        success = adaptor.enhance(Path(skill_dir), api_key)
+
+        if success:
+            print(f"\n✅ Enhancement complete!")
+            print(f"\nNext steps:")
+            print(f"  1. Review: {Path(skill_dir) / 'SKILL.md'}")
+            print(f"  2. If you don't like it, restore backup: {Path(skill_dir) / 'SKILL.md.backup'}")
+            print(f"  3. Package your skill:")
+            print(f"     skill-seekers package {skill_dir}/ --target {args.target}")
+
         sys.exit(0 if success else 1)
 
+    except ImportError as e:
+        print(f"❌ Error: {e}")
+        print("\nAdaptor system not available. Reinstall skill-seekers.")
+        sys.exit(1)
     except ValueError as e:
         print(f"❌ Error: {e}")
-        print("\nSet your API key:")
-        print("  export ANTHROPIC_API_KEY=sk-ant-...")
-        print("Or provide it directly:")
-        print(f"  skill-seekers enhance {skill_dir} --api-key sk-ant-...")
         sys.exit(1)
     except Exception as e:
         print(f"❌ Unexpected error: {e}")