Add smart auto-upload feature with API key detection

Features:
- New upload_skill.py for automatic API-based upload
- Smart detection: upload if API key available, helpful message if not
- Enhanced package_skill.py with --upload flag
- New MCP tool: upload_skill (9 total MCP tools now)
- Enhanced MCP tool: package_skill with smart auto-upload
- Cross-platform folder opening in utils.py
- Graceful error handling throughout

Fixes:
- Fix missing import os in mcp/server.py
- Fix package_skill.py exit code (now 0 when API key missing)
- Improve UX with helpful messages instead of errors

Tests: 14/14 passed (100%)
- CLI tests: 8/8 passed
- MCP tests: 6/6 passed

Files: +4 new, 5 modified, ~600 lines added

cli/utils.py

@@ -0,0 +1,172 @@
+#!/usr/bin/env python3
+"""
+Utility functions for Skill Seeker CLI tools
+"""
+
+import os
+import sys
+import subprocess
+import platform
+from pathlib import Path
+
+
+def open_folder(folder_path):
+    """
+    Open a folder in the system file browser
+
+    Args:
+        folder_path: Path to folder to open
+
+    Returns:
+        bool: True if successful, False otherwise
+    """
+    folder_path = Path(folder_path).resolve()
+
+    if not folder_path.exists():
+        print(f"⚠️  Folder not found: {folder_path}")
+        return False
+
+    system = platform.system()
+
+    try:
+        if system == "Linux":
+            # Try xdg-open first (standard)
+            subprocess.run(["xdg-open", str(folder_path)], check=True)
+        elif system == "Darwin":  # macOS
+            subprocess.run(["open", str(folder_path)], check=True)
+        elif system == "Windows":
+            subprocess.run(["explorer", str(folder_path)], check=True)
+        else:
+            print(f"⚠️  Unknown operating system: {system}")
+            return False
+
+        return True
+
+    except subprocess.CalledProcessError:
+        print(f"⚠️  Could not open folder automatically")
+        return False
+    except FileNotFoundError:
+        print(f"⚠️  File browser not found on system")
+        return False
+
+
+def has_api_key():
+    """
+    Check if ANTHROPIC_API_KEY is set in environment
+
+    Returns:
+        bool: True if API key is set, False otherwise
+    """
+    api_key = os.environ.get('ANTHROPIC_API_KEY', '').strip()
+    return len(api_key) > 0
+
+
+def get_api_key():
+    """
+    Get ANTHROPIC_API_KEY from environment
+
+    Returns:
+        str: API key or None if not set
+    """
+    api_key = os.environ.get('ANTHROPIC_API_KEY', '').strip()
+    return api_key if api_key else None
+
+
+def get_upload_url():
+    """
+    Get the Claude skills upload URL
+
+    Returns:
+        str: Claude skills upload URL
+    """
+    return "https://claude.ai/skills"
+
+
+def print_upload_instructions(zip_path):
+    """
+    Print clear upload instructions for manual upload
+
+    Args:
+        zip_path: Path to the .zip file to upload
+    """
+    zip_path = Path(zip_path)
+
+    print()
+    print("╔══════════════════════════════════════════════════════════╗")
+    print("║                     NEXT STEP                            ║")
+    print("╚══════════════════════════════════════════════════════════╝")
+    print()
+    print(f"📤 Upload to Claude: {get_upload_url()}")
+    print()
+    print(f"1. Go to {get_upload_url()}")
+    print("2. Click \"Upload Skill\"")
+    print(f"3. Select: {zip_path}")
+    print("4. Done! ✅")
+    print()
+
+
+def format_file_size(size_bytes):
+    """
+    Format file size in human-readable format
+
+    Args:
+        size_bytes: Size in bytes
+
+    Returns:
+        str: Formatted size (e.g., "45.3 KB")
+    """
+    if size_bytes < 1024:
+        return f"{size_bytes} bytes"
+    elif size_bytes < 1024 * 1024:
+        return f"{size_bytes / 1024:.1f} KB"
+    else:
+        return f"{size_bytes / (1024 * 1024):.1f} MB"
+
+
+def validate_skill_directory(skill_dir):
+    """
+    Validate that a directory is a valid skill directory
+
+    Args:
+        skill_dir: Path to skill directory
+
+    Returns:
+        tuple: (is_valid, error_message)
+    """
+    skill_path = Path(skill_dir)
+
+    if not skill_path.exists():
+        return False, f"Directory not found: {skill_dir}"
+
+    if not skill_path.is_dir():
+        return False, f"Not a directory: {skill_dir}"
+
+    skill_md = skill_path / "SKILL.md"
+    if not skill_md.exists():
+        return False, f"SKILL.md not found in {skill_dir}"
+
+    return True, None
+
+
+def validate_zip_file(zip_path):
+    """
+    Validate that a file is a valid skill .zip file
+
+    Args:
+        zip_path: Path to .zip file
+
+    Returns:
+        tuple: (is_valid, error_message)
+    """
+    zip_path = Path(zip_path)
+
+    if not zip_path.exists():
+        return False, f"File not found: {zip_path}"
+
+    if not zip_path.is_file():
+        return False, f"Not a file: {zip_path}"
+
+    if not zip_path.suffix == '.zip':
+        return False, f"Not a .zip file: {zip_path}"
+
+    return True, None