Define Loop engineering strategy and v0.2 gates

[chriswu727]

What changed

• Define Loop as the controlled execution layer for loop engineering.
• Map Andrew Ng’s agentic coding, developer-feedback, and external-feedback loops to the product.
• Record seven ordered, testable v0.2 iteration gates and the concrete first contract-compiler slice.
• Link the strategy from the README and documentation index.
• Correct the stale comparison claim about real-provider results.
• Pin patched brace-expansion versions after the first CI run exposed GHSA-3jxr-9vmj-r5cp.

Why

The repository already proves a bounded verified inner loop, but it did not yet record how that capability fits into the broader product-development feedback cycle or exactly how v0.2 should advance. This turns the discussion into a durable roadmap with explicit completion gates instead of calendar estimates.

Validation

• make check: 428 API, 16 web, and 14 desktop tests passed; lint and type checks passed.
• pnpm audit --prod: no known vulnerabilities.
• Targeted Prettier check passed for every changed document and workspace file.
• git diff --check passed.
• All four external strategy references returned HTTP 200.

The pre-existing local apps/web/next-env.d.ts modification is intentionally excluded.