fix(examples): support Python CLI invocation on Windows

[JJasonSun]

Summary

The Python batch runner could find calle.cmd during its precheck but still launch bare calle, causing WinError 2 on Windows. Use one executable resolver for prechecks, CLI launch, and npm installation. Preserve explicit relative paths and Windows backslashes, and report missing or non-executable commands clearly.

batch runner → resolved executable path → CLI auth status
Python integration guide → existing Node launcher with JSON stdin

Add Windows/Python troubleshooting and invocation guidance, linked from the CLI install guide, example index, and batch runner README. Keep direct MCP examples distinct from CLI integrations. Refs CALLE-AI/awesome-phone-call-agents#788.

Evidence

• Before: m15000854110-jpg's Windows test shows bare calle --help fails from Python while calle.cmd --help succeeds. The batch runner discarded its resolved path and parsed Windows paths using POSIX escaping.
• After: Regression tests cover resolved executable use, missing commands, paths with spaces/backslashes, a real Windows .cmd launch, and the documented Node launcher example. CI runs command tests on Windows and batch-runner tests on Linux.
• Local macOS tests: 11 passed, 1 Windows-only test skipped. The actual CLI auth-status invocation returned usable credentials without placing a call. Version consistency and diff checks passed. The latest Linux and Windows CI passed; tests cover explicit relative paths with a same-named PATH executable, a real Windows .cmd launch, and the documented Python launcher example.

Merge Danger

Door: Two-way. Revert the example and documentation changes if needed.

Blast Radius: Examples. Batch-runner command launching changes; CLI runtime and public APIs remain unchanged. No package release or changeset is needed because the example is not packaged.