feat(config): make approval timeout configurable (support timeout_s=0 for unlimited) (#1823)

[bloodycoder]

Summary

Implements #1823 by making approval request timeout configurable.

What changed

1. Added approval.timeout_s in config (default: 300).
2. Runtime behavior:
   • timeout > 0: finite timeout via existing timeout path
   • timeout == 0: wait indefinitely
   • internal None: still treated as unlimited mode
3. Added validation for timeout values:
   • reject negative values
   • reject non-finite values (NaN, Inf, -Inf)
4. Wired timeout from config into shared approval state so subagents inherit the same behavior.
5. Updated EN/ZH config docs with unified semantics.

Files changed

• src/kimi_cli/config.py
• src/kimi_cli/approval_runtime/runtime.py
• src/kimi_cli/soul/approval.py
• src/kimi_cli/soul/agent.py
• tests/core/test_config.py
• tests/core/test_approval_runtime.py
• tests/core/test_approval_timeout_config.py
• docs/en/configuration/config-files.md
• docs/zh/configuration/config-files.md

Expected behavior

• Default remains 300s.
• Users can set custom finite timeout via approval.timeout_s.
• approval.timeout_s = 0 means unlimited wait.

Test plan

Added/updated tests for:

• config default/valid/invalid timeout parsing
• runtime timeout behavior (300, 0, cancellation in unlimited mode)
• timeout config injection + subagent inheritance consistency

Current status

Draft PR due to local environment mismatch:

• local Python: 3.9
• repo requires: >=3.12 (.python-version is 3.14)
• missing tools: uv, tmux

I will rerun and attach full passing logs once environment is aligned.