fix(server): respect tty flag in ExecSandboxInteractive

[letv1nnn]

Summary

ExecSandboxInteractive accepted tty=false in the start request but unconditionally allocated a PTY over SSH, causing processes to always observe terminal-backed file descriptors. This PR threads the tty flag through the interactive exec call chain and guards request_pty and window_change behind it.

Related Issue

Fixes #2228

Changes

• Thread tty: bool through stream_interactive_exec_over_relay and run_interactive_exec_with_russh
• Guard request_pty and window_change behind if tty
• Add unit test for tty=false validation

Reproduction

Used the reproduction script from #2228 to verify behavior before and after the fix.

Before:

After:

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[johntmyers]

dupe of #2315