chore: prepare 0.7.1 docs and version bump

[rlippmann]

What changed

• Reframed and simplified core project docs around app-controlled state rules in README.md.
• Tightened preprocessor guidance in docs/llm-preprocessor.md and experimental/preprocessor/README.md with clearer mutation-safety and decision handling (passthrough / clarify / update).
• Simplified demo framing and interpretation wording in demos/README.md and docs/demos-results.md.
• Simplified integration and example docs (Open WebUI, LiteLLM SDK, LiteLLM Proxy, and examples index) to focus on practical host flow.
• Bumped package version from 0.7.0 to 0.7.1 in pyproject.toml and refreshed uv.lock.

Why

• Align release docs with the 0.7.1 message: prompting helps, but some behaviors require explicit app-controlled state rules.
• Make integration behavior easier to apply in real hosts by reducing jargon and clarifying what to do on each compiler decision.
• Publish the docs work under a matching package version.

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)