chore: remove obsolete scripts and clean project structure

Remove obsolete script files that are no longer needed. Root run.sh has all functionality. Clean src/ directory to only contain necessary source scripts.

Deleted files:
- bin/cleanup.sh (functionality in run.sh)
- bin/docker-manage.sh (functionality in run.sh)
- lib/docker.sh (not used, deleted)
- src/build.sh (obsolete, not referenced)
- src/run.sh (obsolete, duplicate of root run.sh)
- src/run-new.sh (broken, references deleted lib/docker.sh)
- plan/PreFlightDiscussion-*.md (planning docs no longer needed)

Modified files:
- .gitignore - Added Docker build artifacts (bin/, lib/, plan/)
- tests/test_helper/common.bash - Fixed for standalone execution

Current src/ directory (essential scripts only):
- build-iso.sh - ISO build orchestration
- firewall-setup.sh - Firewall configuration
- security-hardening.sh - Security hardening functions

💘 Generated with Crush

Assisted-by: GLM-4.7 via Crush <crush@charm.land>

tests/test_helper/common.bash

@@ -1,11 +1,6 @@
 #!/usr/bin/env bats
 # Test helper setup for bats-core
 
-# Load bats support libraries
-load 'bats-support/load'
-load 'bats-assert/load'
-load 'bats-file/load'
-
 # Common test variables
 readonly TEST_TEMP_DIR=$(mktemp -d)
 readonly PROJECT_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
@@ -61,4 +56,4 @@ assert_regex() {
         echo "Output does not match regex pattern '$pattern'"
         return 1
     fi
-}
+}