fix: Improve config path resolution and error messages (fixes #262)

Three critical UX improvements for custom config handling:

1. User config directory support:
   - Added ~/.config/skill-seekers/configs/ to search path
   - Users can now place custom configs in their home directory
   - Path resolution order: exact path → ./configs/ → user config dir → API

2. Better error messages:
   - Show all searched absolute paths when config not found
   - Added get_last_searched_paths() function to track locations
   - Clear guidance on where to place custom configs

3. Auto-create config.json:
   - ConfigManager now creates config.json on first initialization
   - Creates configs/ subdirectory for user custom configs
   - Display shows custom configs directory path

Fixes reported by @melamers in issue #262 where:
- Config path shown by `skill-seekers config` didn't exist
- Unclear where to save custom configs
- Error messages didn't show exact paths searched

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

src/skill_seekers/cli/config_manager.py

@@ -43,15 +43,28 @@ class ConfigManager:
         self.config_file = self.CONFIG_FILE
         self.progress_dir = self.PROGRESS_DIR
         self._ensure_directories()
+
+        # Check if config file exists before loading
+        config_exists = self.config_file.exists()
         self.config = self._load_config()
 
+        # Save config file if it was just created with defaults
+        if not config_exists:
+            self.save_config()
+
     def _ensure_directories(self):
         """Ensure configuration and progress directories exist with secure permissions."""
+        # Create main config and progress directories
         for directory in [self.config_dir, self.progress_dir]:
             directory.mkdir(parents=True, exist_ok=True)
             # Set directory permissions to 700 (rwx------)
             directory.chmod(stat.S_IRWXU)
 
+        # Also create configs subdirectory for user custom configs
+        configs_dir = self.config_dir / "configs"
+        configs_dir.mkdir(exist_ok=True)
+        configs_dir.chmod(stat.S_IRWXU)
+
     def _load_config(self) -> dict[str, Any]:
         """Load configuration from file or create default."""
         if not self.config_file.exists():
@@ -391,6 +404,7 @@ class ConfigManager:
         """Display current configuration summary."""
         print("\n📋 Skill Seekers Configuration\n")
         print(f"Config file: {self.config_file}")
+        print(f"Custom configs dir: {self.config_dir / 'configs'}")
         print(f"Progress dir: {self.progress_dir}\n")
 
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