docs: rewrite project documentation for clarity

[BR-322]

Summary

• Rewrite the README around project intent, execution flow, evaluation limits, current status, security, and practical setup.
• Rewrite the Cloud Run broker guide and tighten all four active architecture decision records.
• Replace the package description with the same plain-language project positioning.
• Remove metaphor-heavy and stock AI-generated phrasing from the active documentation.

Why

The previous README assumed familiarity with AlphaEvolve, Gate Runner, and quantitative evaluation terminology. It explained the implementation before clearly explaining the project’s purpose. Some status and scoring language had also become inaccurate as the implementation progressed.

This rewrite gives new readers a direct explanation of the experiment while preserving the rigor needed for security, reproducibility, and evaluation design.

Technical clarifications

• Candidate processes do not receive future observations, but the fixed evaluation windows are reused during a search and are not an untouched outer holdout.
• PBO is currently reported as a diagnostic rather than used directly in reward.
• Invalid proposals remain in DSR’s trial count; PBO and behavioral-diversity diagnostics use valid results.
• Cloud Run executor parity is recorded as completed rather than pending.

Validation

• uv run ruff check .
• uv run mypy src
• uv run pytest — 69 passed, 5 environment-dependent tests skipped
• uv lock --check
• repository hygiene check
• local Markdown-link check