0.3.0: Docker image, connection docs, internal refactor

[crp4222]

• Docker: official multi-arch image at ghcr.io/crp4222/privaite, drop-in for OpenAI.
• Internal refactor: shared abstractions for the ML detectors, Presidio recognizers and detector configs; extracted the streaming drain, endpoint helpers and fuzzy matcher. No behavior change (241 tests green, benchmark unchanged).
• Docs: clearer Open WebUI / Docker connection setup (which URL, which key).

Verified end-to-end on this branch: proxy (content, streaming, tool-calls, reasoning) and the Open WebUI filter both restore correctly live; anonymous docker pull + run works; pyscn health 65 to 73.