Add cross-SDK parity validation, expand Python public API tests, and add repo Start Here map

[GsCommand]

Motivation

• Prove cross-SDK parity by running the same verification fixtures through both SDKs and making any drift loudly fail CI.
• Strengthen Python API credibility with intentional, deterministic unit tests that cover the public export surface, client configuration, verb methods, and local verification behavior.
• Improve newcomer navigation by adding a concise root-level "Start Here" map and lightweight guide stubs so links in the README are actionable.

Description

• Add a manifest-driven parity system and runner that ensures both SDKs verify the identical test_vectors and that recomputed hashes, signer resolution, and pass/fail outcomes match; key assets are test_vectors/parity_manifest.json, scripts/parity-check.mjs, scripts/parity-ts-report.mjs, and python-sdk/tests/parity_report.py.
• Add a CI job parity-check (.github/workflows/parity-check.yml) which installs/builds the TypeScript SDK, installs Python dev deps, and executes the root parity check so mismatches cause the job to fail.
• Expand and replace the lightweight Python public API test with a purposeful suite at python-sdk/tests/test_public_api.py that asserts importable symbols, create_client() behavior, presence and callability of verb methods, response envelope shape, verify_receipt contract, and a fast mocked end-to-end vector-backed flow.
• Add a short repository "Start Here" map to README.md and lightweight guide stubs (CONTRIBUTING.md, MAINTAINER_GUIDE.md, RELEASE_GUIDE.md, CHANGELOG.md, and test_vectors/README.md) to make navigation immediate and explicit.

Testing

• TypeScript: ran npm install / npm run build / npm test in typescript-sdk, and all unit and runtime tests passed locally (TS build and test suite succeeded).
• Python: ran PYTHONPATH=. python -m pytest and the full Python test suite passed (pytest succeeded), but pip install -e '.[dev]' and python -m build failed in this environment due to missing build-time dependencies (network/proxy prevented fetching setuptools / build), so packaging steps failed here but are covered by the CI job which installs deps in a clean runner.
• Parity: ran node scripts/parity-check.mjs which invoked both scripts/parity-ts-report.mjs and python-sdk/tests/parity_report.py; the reports were normalized and compared and the parity check passed locally, printing per-vector PASS/FAIL lines and exiting non-zero on mismatch (the workflow is configured to run this check in CI).

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Codex Task