Reframe README as a QCA best-practice reference

[anchenqlw]

What changed

• Reframed the bilingual README around Qoder Cloud Agents rather than Operra product marketing.
• Removed the “Why Operra” and “why now” narratives.
• Explained the QCA capabilities that make the reference product possible.
• Documented the two QCA patterns used in the application: task execution and a custom-tool-powered workspace operator.
• Added a source map and reusable guidance for developers building their own QCA products.

Why

Operra should serve as a concrete QCA best-practice reference. The primary recommendation is QCA; Operra is the runnable example showing how a thin product layer can turn QCA sessions, cloud execution, GitHub collaboration, event streams, and deployments into a useful product.

Validation

• python -m pytest -q tests/test_public_source_release.py — 6 passed
• public export validation passed
• gitleaks scan of the 1.44 MB public tree found no leaks
• staged diff check passed