fix: Resolve all linting errors from ruff

Fix 145 linting errors across CLI refactor code:

Type annotation modernization (Python 3.9+):
- Replace typing.Dict with dict
- Replace typing.List with list
- Replace typing.Set with set
- Replace Optional[X] with X | None

Code quality improvements:
- Remove trailing whitespace (W291)
- Remove whitespace from blank lines (W293)
- Remove unused imports (F401)
- Use dictionary lookup instead of if-elif chains (SIM116)
- Combine nested if statements (SIM102)

Files fixed (45 files):
- src/skill_seekers/cli/arguments/*.py (10 files)
- src/skill_seekers/cli/parsers/*.py (24 files)
- src/skill_seekers/cli/presets/*.py (4 files)
- src/skill_seekers/cli/create_command.py
- src/skill_seekers/cli/source_detector.py
- src/skill_seekers/cli/github_scraper.py
- tests/test_*.py (5 test files)

All files now pass ruff linting checks.

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

tests/test_create_integration_basic.py

@@ -5,10 +5,6 @@ and routes to the correct scrapers without actually scraping.
 """
 
 import pytest
-import tempfile
-import os
-from pathlib import Path
-
 
 class TestCreateCommandBasic:
     """Basic integration tests for create command (dry-run mode)."""
@@ -124,7 +120,6 @@ class TestCreateCommandBasic:
         assert '--preset' in result.stdout
         assert '--dry-run' in result.stdout
 
-
 class TestBackwardCompatibility:
     """Test that old commands still work."""