docs: distribution and deployment design doc

[henrycgbaker]

Goal

Add design doc covering how pragmata is distributed and deployed in production. Separated from the annotation stack lifecycle doc (PR #175).

Scope

• distribution-and-deployment.md — artefact strategy (PyPI primary, container image deferred to v0.2+), per-tool deployment shapes, the case against Docker-outside-of-Docker, persistence/backup, and TLS/reverse-proxy topology for a self-hosted annotation campaign
• README.md — index entry

Implementation

Design-only PR. No code changes.

Key decisions documented:

• PyPI package is the primary artefact for v0.1; container image deferred
• DooD explicitly ruled out - wrong security profile for our deployment shape
• Escape hatch documented: operators can run the shipped compose file directly without the CLI
• Argilla port binds to localhost only by default to avoid accidental public exposure

References

• ADR-0003 (infra: self-hosted only)
• ADR-0007 (packaging & invocation surface)
• Companion PR docs: annotation stack lifecycle design doc #175 (annotation stack lifecycle)
• Companion PR docs(config): config and settings design doc #162 (config & settings)