fix: spill long system prompts on Windows

[MukundaKatta]

Fixes #883

• rewrite oversized inline --system-prompt and --append-system-prompt args to temporary --*-file args before spawning Claude Code on Windows
• clean up temporary prompt files after close or failed connect
• report Windows WinError 206 as a command-line-length failure instead of CLINotFoundError when the CLI path exists

Checks:

• uv run --extra dev pytest tests/test_transport.py -q
• uv run --extra dev ruff check src/claude_agent_sdk/_internal/transport/subprocess_cli.py tests/test_transport.py
• uv run --extra dev ruff format --check src/claude_agent_sdk/_internal/transport/subprocess_cli.py tests/test_transport.py
• git diff --check