Preserve an explicit max_turns=0 when building the CLI command

[Osamaali313]

Problem

When building the CLI command, --max-turns is gated on a truthy check, while every other numeric option uses is not None:

if self._options.max_turns:                       # truthy — drops 0
    cmd.extend(["--max-turns", str(self._options.max_turns)])
...
if self._options.max_budget_usd is not None:      # preserves 0
    cmd.extend(["--max-budget-usd", str(self._options.max_budget_usd)])
if self._options.task_budget is not None:
    cmd.extend(["--task-budget", str(self._options.task_budget["total"])])
...
elif self._options.max_thinking_tokens is not None:
    cmd.extend(["--max-thinking-tokens", str(self._options.max_thinking_tokens)])
if self._options.effort is not None:
    cmd.extend(["--effort", ...])

So a caller that explicitly sets max_turns=0 has the flag silently omitted, and the CLI falls back to its default turn limit — the opposite of the explicit request. An explicitly-provided option shouldn't be discarded just because its value is 0.

Fix

Match the sibling numeric options:

if self._options.max_turns is not None:
    cmd.extend(["--max-turns", str(self._options.max_turns)])

Reproduction

option value	before	after
max_turns=0	(flag omitted) ❌	--max-turns 0 ✅
max_budget_usd=0.0	--max-budget-usd 0.0	--max-budget-usd 0.0
max_thinking_tokens=0	--max-thinking-tokens 0	--max-thinking-tokens 0

(max_turns=0 is the only numeric option whose explicit 0 is currently lost.)

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