fix: prevent goroutine leak in terminal exec timeout handling

[haosenwang1018]

Problem

When getExecResult times out via ctx.Done(), the function returns but leaves a goroutine blocked on io.Copy(&dst, resp.Reader). The connection (resp) is only closed by defer after the function returns, but by that point the goroutine is already leaked — io.Copy may remain blocked even after resp.Close() because the close races with the blocked read.

Each timed-out command leaks one goroutine and its associated resources (#108).

Fix

• Close resp before waiting for the goroutine on timeout, which unblocks io.Copy
• Wait for the goroutine (<-done) after closing to ensure clean shutdown
• On the normal path, close resp immediately after copy completes
• Remove defer resp.Close() since both paths now close explicitly

Before

timeout → return → defer resp.Close() → goroutine still blocked on io.Copy

After

timeout → resp.Close() → io.Copy returns → <-done → return (no leak)

Fixes #108

[asdek]

hey @haosenwang1018

these changes was included by #124 into temporary branch
https://github.com/vxcontrol/pentagi/commits/feature/project_improvements/

it'll be added today in the master branch

thank you for suggestion!