docs: mark environment variable runtime scopes

[jiangyuer018]

Closes #133\n\n## Problem\nThe README environment-variable table did not say whether each variable is read by the native Rust runtime, the legacy Python/TypeScript runtimes, or both.\n\n## Change\nAdded a Scope column for every row, split mixed-scope rows where needed, and documented the scope labels.\n\n## Validation\n- git diff --check

[NekomyaDev]

Thank you for working on this! Several scope annotations in the Environment Variables table need corrections before merging:

1. NUDGE_REPAIR_BUDGET: Marked as python/TS, but it is only read in the Python runtime (runtime/nudge_runtime/__init__.py:1494) and is absent from runtime/nudge_runtime.ts. This should be python.
2. NUDGE_OTEL and NUDGE_OTEL_ENDPOINT: Marked as python/TS, but they are only implemented in Python (runtime/nudge_runtime/__init__.py:727, 749) and not in TypeScript or native Rust. These should be python.
3. NUDGE_DECISION_SERVERS and NUDGE_DECISION_CACHE: Marked as both, but neither is supported in the native Rust runtime (crates/ has only deterministic fake decisions; live servers and caching are Python/TS only). Marking them as both is inaccurate.
4. CI Status: pre-commit.ci is currently failing on this branch.

Please update the annotations and rebase/fix CI so we can get this landed.

[jiangyuer018]

Updated the environment variable scope annotations as requested:

• NUDGE_REPAIR_BUDGET is now python.
• NUDGE_OTEL and NUDGE_OTEL_ENDPOINT are now python.
• NUDGE_DECISION_SERVERS and NUDGE_DECISION_CACHE are now python/TS.

Also applied the whitespace and EOF fixes reported by pre-commit.ci. The new pre-commit.ci check is passing on commit 792dc53.