docs: align Python docs narrative

[rlippmann]

What changed

• reoriented the Python README so explanatory material comes before operational/reference material
• shifted the README examples and opening language toward deterministic conversational state authority instead of guardrail-first framing
• added a short docs/architecture.md note that defines acquisition, authority, application, classification, and composition boundaries
• updated the docs index plus examples/demo index text to make premise, controller, and state-authority behavior easier to understand on first read
• applied small follow-up wording cleanups and moved the controller quick example under the controller API section

Why

• the Python repo’s first impression had drifted toward persistent guardrails, tool filtering, and prompt reinjection framing
• these docs changes make the package read more clearly as a deterministic conversational state authority without changing engine behavior, APIs, or result shapes

Checklist

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