--dry-run flag deletes files during update

[fgrehm]

Description:

When running update with the --dry-run flag, files are actually deleted during the cleanup phase, even though the script displays "DRY RUN - No files will be actually modified". The deleted files are not recreated, resulting in data loss.

How it happens:

The bug is in scripts/project-update.sh, but it can be triggered when running project-install.sh on an existing installation (which automatically calls the update script).

Reproduction Steps:

1. Install Agent OS in a project: ~/agent-os/scripts/project-install.sh
2. Later, run with dry-run: ~/agent-os/scripts/project-install.sh --dry-run
3. Script detects existing installation and runs update
4. Observe: Files are actually deleted despite dry-run flag
5. Check git status: Shows deleted files in agent-os/standards/, .claude/agents/, etc.

Expected Behavior:

Dry-run mode should preview changes without modifying any files.

Actual Behavior:

The perform_update_cleanup() function in scripts/project-update.sh has 7 rm -rf commands without DRY_RUN checks. The cleanup runs unconditionally, then the update phase respects dry-run mode and doesn't recreate files.

Files deleted:

• agent-os/standards/
• agent-os/commands/
• .claude/agents/agent-os/
• .claude/commands/agent-os/
• .claude/skills/ (Agent OS skills)
• agent-os/roles/ (legacy)

Impact:

Users lose data when trying to safely preview updates. Makes dry-run mode unreliable.

Fix:

I have a fix ready that wraps all deletion operations with dry-run checks in #245