feat: add CONFIG_ARGUMENTS and fix _route_config for unified scraper parity

Previously _route_config only forwarded --dry-run, silently dropping
all enhancement workflows, --merge-mode, and --skip-codebase-analysis.

Changes:
- arguments/create.py: add CONFIG_ARGUMENTS dict with merge_mode and
  skip_codebase_analysis; wire into get_source_specific_arguments(),
  get_compatible_arguments(), and add_create_arguments(mode='config')
- create_command.py: fix _route_config to forward --fresh, --merge-mode,
  --skip-codebase-analysis, and all 4 workflow flags; add --help-config
  handler (skill-seekers create --help-config) matching other help modes
- parsers/create_parser.py: add --help-config flag for unified CLI parity
- tests/test_create_arguments.py: import CONFIG_ARGUMENTS; update config
  source tests to assert correct content instead of empty dict

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/skill_seekers/cli/parsers/create_parser.py

@@ -83,6 +83,12 @@ Presets: -p quick (1-2min) | -p standard (5-10min) | -p comprehensive (20-60min)
             help="Show PDF extraction specific options",
             dest="_help_pdf",
         )
+        parser.add_argument(
+            "--help-config",
+            action="store_true",
+            help="Show multi-source config file specific options",
+            dest="_help_config",
+        )
         parser.add_argument(
             "--help-advanced",
             action="store_true",