refactor: unify documentation CLI configuration

[AlexanderLanin]

What this achieves

Documentation Bazel wrappers and cli.py now share one versioned SCORE_DOCS_CONFIG JSON contract for target configuration. Runtime workspace, runfiles, and CI context remains in the process environment.

Why this is necessary

The previous split across individual environment variables and SPHINX_EXTRA_OPTS made configuration assembly difficult to validate and allowed path-resolution and duplicate-option bugs between interactive and sandboxed Needs builds. A single structured payload makes the contract explicit and versionable.

What changed

• Build version-1 payloads for interactive binaries and Needs actions.
• Resolve runfiles and execution-root paths from the action context.
• Generate Sphinx defines, live-preview watches, and cache/output behavior from the payload.
• Remove the legacy CLI configuration transport and preserve extension configuration through Sphinx defines.
• Add payload validation, path-resolution, merged-Needs, mount-watching, malformed-version, and diagnostics coverage.
• Document the payload contract.