fix: resolve all ruff linting errors (W293, F401, B904, UP007, UP045, E741, SIM102, SIM117, ARG)

Auto-fixed (whitespace, imports, type annotations):
- codebase_scraper.py: W293 blank lines with whitespace
- doc_scraper.py: W293 blank lines with whitespace
- parsers/extractors/__init__.py: W293
- parsers/extractors/base_parser.py: W293, UP007, UP045, F401

Manual fixes:
- enhancement_workflow.py: B904 raise without `from exc`, remove unused `os` import
- parsers/extractors/quality_scorer.py: E741 ambiguous var `l` → `line`
- parsers/extractors/rst_parser.py: SIM102 nested if → combined conditions (x2)
- pdf_scraper.py: F821 undefined `logger` → `print()` (consistent with file style)
- mcp/tools/workflow_tools.py: ARG001 unused `args` → `_args`
- tests/test_workflow_runner.py: ARG005 unused lambda args → `_a`/`_kw`, ARG001 `kwargs` → `_kwargs`
- tests/test_workflows_command.py: SIM117 nested with → combined with (x2)

All 1922 tests pass.

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

src/skill_seekers/cli/enhancement_workflow.py

@@ -24,7 +24,6 @@ Usage:
 
 import json
 import logging
-import os
 from dataclasses import dataclass, field
 from datetime import datetime
 from importlib.resources import files as importlib_files
@@ -145,11 +144,11 @@ class WorkflowEngine:
                 pkg_ref = importlib_files("skill_seekers.workflows").joinpath(bare_name)
                 yaml_text = pkg_ref.read_text(encoding="utf-8")
                 logger.info(f"📋 Loading bundled workflow: {bare_name}")
-            except (FileNotFoundError, TypeError, ModuleNotFoundError):
+            except (FileNotFoundError, TypeError, ModuleNotFoundError) as exc:
                 raise FileNotFoundError(
                     f"Workflow '{yaml_ref.stem}' not found. "
                     "Use 'skill-seekers workflows list' to see available workflows."
-                )
+                ) from exc
 
         if resolved_path is not None:
             logger.info(f"📋 Loading workflow: {resolved_path}")