fix(voice): reject non-positive audio frame rates

[hsusul]

Summary

_buffer_to_audio_file validates sample width, buffer dtype, channel count, and multichannel frame completeness, but previously did not validate the frame rate. A zero or negative frame_rate reached wave.setframerate and surfaced as a low-level wave.Error instead of the UserError used by the adjacent input validations.

This adds an up-front frame_rate <= 0 check so invalid rates fail consistently and actionably. Valid audio conversion is unchanged.

The earlier negative-history-limit changes have been removed to preserve the released SQLite behavior documented by v0.20.0 and #4001.

Test plan

• Added test_audio_input_rejects_non_positive_frame_rate, parametrized over 0 and -8000.
• uv run pytest -q tests/voice/test_input.py — 24 passed.
• env UV_DEFAULT_INDEX=https://pypi.org/simple bash .agents/skills/code-change-verification/scripts/run.sh — passed:
  • Ruff format: 897 files unchanged.
  • Ruff lint: passed.
  • mypy and Pyright: passed.
  • Full test suite: passed.
• git diff --check — passed.

Issue number

None.

Checks

• I've added new tests, if relevant
• I've run .agents/skills/code-change-verification/scripts/run.sh
• I've confirmed all verification steps pass
• If using Codex, I've run /review before submitting this PR

[seratch]

@hsusul Thanks for suggesting this but your another PR #4383 is quite similar, so we may want to avoid taking our time to review these small PRs one by one. If you don't mind, can you do thorough investigation to detect similar opportunities to improve and include all of them in this PR?

[seratch]

Thanks for expanding this after the earlier review. I reran the new tests against the merge base: the frame-rate test demonstrates a real, bounded exception-contract gap, but the negative-history work should not be included. v0.20.0 and #4001 intentionally preserve SQLite's historical negative-limit behavior (limit=-1 returns all items), while this branch changes it to an empty history. The OpenAI-specific negative case is not a demonstrated supported scenario, and silently treating invalid negative input as no history is not a safe cross-backend compatibility fix.

Please keep the frame-rate validation and regression test, remove both negative-limit commits and their tests, and update the title and description to the remaining voice scope. This preserves released session behavior while retaining the demonstrated improvement.