Fix Windows existing-instance startup

[nicoloboschi]

Summary

• remove the obsolete pg_textsearch documentation and installer
• replace Windows tasklist process probing with a direct Win32 handle query
• add a timeout-bound Windows regression test for restarting an existing instance

Root cause

Starting an existing instance called tasklist synchronously before PostgreSQL setup emitted any output. If that external command blocked, pg0 start appeared to hang indefinitely.

Validation

• cargo metadata --no-deps --format-version 1
• Python syntax parse for the updated test module
• git diff --check

The local macOS host cannot complete a Windows cross-build because its C cross-toolchain lacks Windows headers; the GitHub Windows CI job will execute the regression test.