Tighten docs, add contributor/release/versioning guides, and fix real key-rotation tests

[GsCommand]

Motivation

• Remove misleading internal root docs and make it explicit which docs are for maintainers vs external developers.
• Fix a critical correctness gap where key-rotation was not exercised by real fixtures and ENS routing logic.
• Make the repo usable by new contributors without tribal knowledge (build/test ordering and CLI parity clarified).
• Provide reproducible release automation and an explicit versioning policy so publishes are enforced rather than ad-hoc.

Description

• Renamed DEVELOPER_EXPERIENCE.md → MAINTAINER_GUIDE.md and DEPLOYMENT_GUIDE.md → RELEASE_GUIDE.md, and rewrote the first paragraph of each to state the intended audience and who they are not for.
• Added CONTRIBUTING.md, VERSIONING.md, and a root package.json with test:full to document and script build/test ordering for runtime tests.
• Introduced .github/workflows/release.yml to run TS + Python CI, build artifacts, validate packages, and publish on tag/release events.
• Replaced misleading fixture naming and added real rotation fixtures: public_key_v1_base64.txt, public_key_v2_base64.txt, receipt_valid_v1.json, receipt_valid_v2.json, receipt_removed_kid.json, and test_vectors/README.md; removed the old receipt_malformed_pubkey.json.
• Implemented real ENS key-routing by kid in TypeScript (resolveSignerKey now accepts requestedKid) and mirrored the behavior in Python, and updated helpers and runtime tests to exercise v1-after-v2, v2-current, wrong kid, and removed kid cases.
• Clarified CLI design and Python/TS CLI asymmetry in docs and adjusted CLI help strings and smoke tests to match the explicit design (verb-specific vs generic call, and verify input expectations).

Testing

• Ran TypeScript build and unit/template/CLI smoke suites: npm install → npm run build → npm run test succeeded (TS unit/tests + template subtests passed, CLI smoke adjusted and passed).
• Ran runtime cross-SDK tests via the new root script: npm run test:full succeeded, exercising the updated ENS rotation tests (runtime tests passed).
• Ran Python unit tests: cd python-sdk && pytest succeeded (all Python verification tests passed).
• Python packaging validation (python -m build and python -m twine check dist/*) could not be executed in this environment due to missing build/twine modules, so PyPI artifact validation remains to be exercised in CI.

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Codex Task