🚀 MAJOR: Full migration to Just modules with modern features

BREAKING CHANGES:
- Complete restructure to Just module architecture (requires Just 1.31.0+)
- Command syntax changed: 'just postgres-sql' → 'just postgres sql'
- Import syntax changed: import → mod declarations

NEW FEATURES:
✨ Module-based architecture with optional modules
✨ Built-in Just colors ({{RED}}, {{GREEN}}, etc.) replace custom variables
✨ Enhanced [confirm] attributes for all destructive operations
✨ Organized [group('name')] attributes for better UX
✨ Modern justfile with comprehensive help system
✨ Updated documentation with migration guide

MODULES:
📦 postgres/    - PostgreSQL operations (sql, check, create-database, etc.)
📦 mysql/       - MySQL operations (sql, check, create-user, etc.)
📦 volumes/     - Volume management (clean-all, remove, list)
📦 container/   - Container operations (start, stop, logs, shell, exec)
📦 registry/    - Registry auth (login, logout, check)
📦 images/      - Image operations (build, push, pull, tag, clean)

USAGE:
just postgres sql "SELECT version();"
just volumes clean-all
just images build myapp

This is Just Commons v2.0 - a complete modernization using all of Just's latest features.

registry/mod.just

@@ -0,0 +1,65 @@
+# Container registry authentication and management
+
+# Login to container registry
+[group('registry')]
+login:
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    if [ -z "${GITHUB_USERNAME:-}" ] || [ -z "${GITHUB_TOKEN:-}" ]; then
+        echo "{{BOLD}}{{RED}}Error:{{NORMAL}} GITHUB_USERNAME and GITHUB_TOKEN environment variables must be set" >&2
+        echo "{{YELLOW}}Please set these in your .env file or environment{{NORMAL}}" >&2
+        exit 1
+    fi
+
+    runtime=$(just _detect_runtime)
+    registry="${REGISTRY:-ghcr.io}"
+
+    echo -e "{{BLUE}}Logging into registry: $registry{{NORMAL}}"
+    echo "$GITHUB_TOKEN" | $runtime login "$registry" -u "$GITHUB_USERNAME" --password-stdin
+
+    echo -e "{{GREEN}}✓ Successfully logged into $registry{{NORMAL}}"
+
+# Logout from container registry
+[group('registry')]
+logout:
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    runtime=$(just _detect_runtime)
+    registry="${REGISTRY:-ghcr.io}"
+
+    echo -e "{{BLUE}}Logging out from registry: $registry{{NORMAL}}"
+    $runtime logout "$registry"
+
+    echo -e "{{GREEN}}✓ Successfully logged out from $registry{{NORMAL}}"
+
+# Check registry authentication status
+[group('registry')]
+check:
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    runtime=$(just _detect_runtime)
+    registry="${REGISTRY:-ghcr.io}"
+
+    echo -e "{{BLUE}}Registry Configuration:{{NORMAL}}"
+    echo -e "{{YELLOW}}Registry:{{NORMAL}} $registry"
+    echo -e "{{YELLOW}}Username:{{NORMAL}} ${GITHUB_USERNAME:-'Not set'}"
+    echo -e "{{YELLOW}}Token:{{NORMAL}} ${GITHUB_TOKEN:+'Set'}${GITHUB_TOKEN:-'Not set'}"
+    echo ""
+
+    echo -e "{{BLUE}}Testing registry authentication...{{NORMAL}}"
+
+    # Check if we can access the registry
+    if echo "$GITHUB_TOKEN" | $runtime login "$registry" -u "$GITHUB_USERNAME" --password-stdin >/dev/null 2>&1; then
+        echo -e "{{GREEN}}✓ Registry authentication successful{{NORMAL}}"
+
+        # Show configured registries
+        echo -e "{{BLUE}}Configured registries:{{NORMAL}}"
+        $runtime system info --format "{{{{.RegistryConfig.IndexConfigs}}}}" 2>/dev/null || echo "Registry config not available"
+    else
+        echo -e "{{RED}}✗ Registry authentication failed{{NORMAL}}"
+        echo -e "{{YELLOW}}Please check your GITHUB_USERNAME and GITHUB_TOKEN{{NORMAL}}"
+        exit 1
+    fi