Fix screen multiuser attach permission error

[elyxlz]

Summary

• Fixes the "seteuid: Operation not permitted" error when using nx attach with remote servers
• Removes the problematic sudo -u nexus screen -X acladd command
• Pre-grants screen session access to all users at creation time instead

Problem

After adding SSH port support, nx attach started failing with:

seteuid: Operation not permitted
Connection to <host> closed.
SSH attach failed (exit 1)

Root Cause: The sudo -u nexus screen -X acladd command creates a privilege conflict with screen's setuid mechanism. When screen has the setuid bit set (required for multiuser mode), wrapping it in sudo -u confuses screen's internal privilege management, causing the seteuid() syscall to fail.

Solution

Based on extensive research of GNU screen documentation and community solutions:

Before: Runtime ACL manipulation via sudo -u nexus screen -X acladd <user>
After: Pre-configure multiuser permissions at session creation time

Changes

File: src/nexus/server/core/job.py

• Added aclchg :+rwx "#" to SCREENRC_CONTENT (line 37)
• This grants read/write/execute permissions to all users when the session is created

File: src/nexus/cli/jobs.py

• Removed the entire first SSH call that ran sudo -u nexus screen -X acladd
• Users can now attach directly since permissions are pre-granted

Why This Works

1. Avoids privilege conflicts: No runtime sudo wrapper interfering with screen's setuid
2. Simpler architecture: Permissions set once at creation, not on every attach
3. More reliable: Follows GNU screen's recommended pattern for multiuser sessions
4. Better performance: One less SSH round-trip on every attach

Test Plan

• Create a new job on remote server
• Verify nx attach <job_id> works without seteuid errors
• Verify multiuser sessions work correctly
• Run uv run pyright to verify type safety (passes ✓)

Version

Bumped to 0.5.31b1 (beta) as this changes core screen session behavior.

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