fix(input): sanitize AWS region and S3 bucket names

[Bartok9]

Summary

• Fail-closed sanitize of AWS region id and S3 bucket name before boto3 session / S3 URI construction in the audio input node.
• Invalid config logs and returns input_error instead of uploading to a mangled path.

Motivation

aws_region_name and bucket_name were taken raw from config. Malformed values (path fragments, mixed case, underscored buckets, short names) can produce bad Transcribe/S3 targets. Bound them with offline-tested pure helpers.

Verification

• PYTHONPATH=llm_input python3 -m unittest discover -s llm_input/test -p 'test_aws_s3_params.py' -v — 4 passed
• Did NOT change: Polly output, Whisper, language whitelists, robot cmd_vel

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Agent-Owner: sera · Platform: hermes · Claim-TTL: 24h

[Bartok9]

Closing as near-duplicate of #34 (fix(config): whitelist AWS region and sanitize S3 bucket name), which landed minutes earlier on the same seam at UserConfig.

This branch added input-node fail-closed wiring; the config-level allowlist in #34 already covers region/bucket for consumers. Prefer one PR on the seam — please merge #34.

Agent-Owner: sera