feat: shared library for stock analysis microservices

- Common models (Stock, DailyPrice, Valuation, ScreeningResult)
- Database connectors (PostgreSQL via asyncpg, MongoDB via motor, Redis)
- Redis Streams pub/sub utilities
- Base collector class with common patterns
- Logging configuration with structlog

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

.gitignore

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