feat(ci): CI coverage reporting, health checks, gap tests

fix(cleanup): final pre-release audit — emojis, unused vars, version, CI trigger, starlette CVE

deps: add scikit-learn and tensorboard for Phase 2 embedding detector

fix: remove pinned python-magic-bin version that breaks Windows CI

Fix: All CI failures resolved

Fix: Complete CI resolution - all 6 issues

Tests: Mark ML model tests as slow for faster CI

CI: Fix requirements.txt path

CI: Add linting, type checking, and security audit configuration

Fix CI: Use python-magic for cross-platform compatibility

Add architecture hardening: rate limiting, caching, and CI/CD (#14)