feat: add automatic cleanup of stale Docker resources

[boffin-dmytro]

Summary

• Automatically detect and remove stale Dream Server containers and networks
• Prevents installation failures caused by leftover resources from previous failed installs
• Non-blocking cleanup with clear user feedback

Rationale

Failed installations leave containers in Created/Exited state and orphaned networks. These stale resources cause cryptic errors on the next install attempt (port conflicts, network conflicts, volume mount issues). Automatic cleanup ensures a clean slate for each installation.

Changes

• Detect all containers with 'dream-' prefix from previous installations
• Remove stale containers (stopped, created, or exited state)
• Clean up orphaned dream-server networks
• Log cleanup actions for transparency
• Non-blocking: cleanup failures don't stop installation

Test Plan

• Verify cleanup detects stale containers from failed install
• Verify cleanup removes containers in all states (Created, Exited, Running)
• Verify cleanup removes orphaned networks
• Verify installation succeeds after cleanup
• Verify cleanup is non-blocking (continues on errors)

[boffin-dmytro]

Closing - will recreate against upstream repo