fix: add trap handlers for tmpfile cleanup in installers

[boffin-dmytro]

Summary

Adds proper trap handlers to ensure temporary files are cleaned up even if installer phases are interrupted.

Changes

• installers/phases/05-docker.sh: Add trap handler for Docker install script cleanup
• installers/phases/07-devtools.sh: Add trap handlers for Node.js and OpenCode install script cleanup

Problem Solved

Temporary files created during installer phases could be left behind if:

• User interrupts installation (Ctrl+C)
• Network timeout causes script termination
• System receives TERM signal during installation

Benefits

• Resource cleanup: Prevents /tmp pollution from interrupted installs
• Security: Removes potentially sensitive install scripts from filesystem
• Reliability: Ensures clean state for retry attempts

Implementation

Uses trap 'rm -f "$tmpfile"' EXIT INT TERM pattern to handle:

• EXIT: Normal script completion (success or failure)
• INT: User interruption (Ctrl+C)
• TERM: System termination signal