Add Prompt Engineering & Linting Tools (90 repos) + Custom Linter

Features Added:
- Custom Python prompt linter (prompt_linter.py)
  - Security checks: injection patterns, PII detection
  - Clarity analysis: vague language, ambiguity, anti-patterns
  - Performance: length, redundancy, token estimation
  - Best practices: examples, output format, context

- Comprehensive guide (PROMPT_LINTING_GUIDE.md)
  - Tool comparisons (Promptfoo, LMQL, Guardrails, Rebuff)
  - Usage examples and integration patterns
  - CI/CD integration, pre-commit hooks
  - Best practices and anti-patterns

- Starred 90 repositories across 8 categories:
  - Prompt Linting & Validation (10)
  - Prompt Injection Detection & Security (15)
  - Prompt Engineering Frameworks (20)
  - Prompt Testing & Evaluation (15)
  - Prompt Optimization & Research (10)
  - LLM Observability & Debugging (10)
  - Prompt Libraries & Templates (10)
  - Advanced Prompting Techniques (10)

- Updated documentation:
  - README.md with Prompt Engineering section
  - STARRED-INDEX.md with comprehensive links
  - Repository count: 3,400+ → 3,500+

Key Tools:
- Promptfoo (35K⭐): Testing & vulnerability scanning
- LangChain (102K⭐): LLM application framework
- AutoGPT (171K⭐): Autonomous GPT-4
- LMQL (4K⭐): Constraint-guided programming
- Guardrails AI: Safety & validation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: Niraj Bajpai