feat(#191): Smart description generation for skill descriptions

Implements hybrid smart extraction + improved fallback templates for
skill descriptions across all scrapers.

Changes:
- github_scraper.py:
  * Added extract_description_from_readme() helper
  * Extracts from README first paragraph (60 lines)
  * Updates description after README extraction
  * Fallback: "Use when working with {name}"
  * Updated 3 locations (GitHubScraper, GitHubToSkillConverter, main)

- doc_scraper.py:
  * Added infer_description_from_docs() helper
  * Extracts from meta tags or first paragraph (65 lines)
  * Tries: meta description, og:description, first content paragraph
  * Fallback: "Use when working with {name}"
  * Updated 2 locations (create_enhanced_skill_md, get_configuration)

- pdf_scraper.py:
  * Added infer_description_from_pdf() helper
  * Extracts from PDF metadata (subject, title)
  * Fallback: "Use when referencing {name} documentation"
  * Updated 3 locations (PDFToSkillConverter, main x2)

- generate_router.py:
  * Updated 2 locations with improved router descriptions
  * "Use when working with {name} development and programming"

All changes:
- Only apply to NEW skill generations (don't modify existing)
- No API calls (free/offline)
- Smart extraction when metadata/README available
- Improved "Use when..." fallbacks instead of generic templates
- 612 tests passing (100%)

Fixes #191

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/generate_router.py

@@ -73,7 +73,7 @@ class RouterGenerator:
 
 ## When to Use This Skill
 
-{self.base_config.get('description', f'Use for {self.router_name} development and programming.')}
+{self.base_config.get('description', f'Use when working with {self.router_name} development and programming')}
 
 This is a router skill that directs your questions to specialized sub-skills for efficient, focused assistance.
 
@@ -156,7 +156,7 @@ Simply ask your question and mention the topic. The router will find the right s
 
         router_config = {
             "name": self.router_name,
-            "description": self.base_config.get('description', f'{self.router_name.title()} documentation router'),
+            "description": self.base_config.get('description', f'Use when working with {self.router_name} documentation (router for multiple sub-skills)'),
             "base_url": self.base_config['base_url'],
             "selectors": self.base_config.get('selectors', {}),
             "url_patterns": self.base_config.get('url_patterns', {}),