Implement high-impact improvements based on ChatGPT feedback

SAFETY IMPROVEMENTS:
- Strengthen safety warnings with 🚨 emoji and mandatory confirmation
- Add BOOTC_CONFIRM_DISK_WIPE=1 requirement for destructive operations
- Add 10-second sleep before exit to prevent accidental execution
- Emphasize experimental nature and data loss risks

COMPATIBILITY MATRIX:
- Create detailed version compatibility table with specific versions
- Add feature compatibility by bootc version
- Include kernel requirements for each feature
- Document experimental flags and their version requirements

KERNEL REQUIREMENTS:
- Add comprehensive kernel feature checklist
- Include verification commands for kernel features
- Specify exact kernel versions for different features
- Add EROFS, composefs, overlayfs, fsverity requirements

LICENSING:
- Add Apache 2.0 LICENSE file with SPDX identifier
- Remove ambiguity about licensing terms

CI/AUTOMATION:
- Add GitHub Actions workflow for automated testing
- Test base image building and validation
- Test nginx layer creation
- Validate documentation structure
- Check for broken links and markdown syntax

This addresses the most critical feedback while maintaining focus
on what actually works (Sid/Forky + modern OSTree).

building/base-images-wo-bootc.md

@@ -863,13 +863,19 @@ IMAGE_NAME="${1:-debian-bootc-base:latest}"
 TARGET_ROOT="${2:-/mnt/sysroot}"
 
 # Safety check for destructive operations
-if [ "${TARGET_ROOT}" != "/mnt/sysroot" ] && [ -z "${BOOTC_I_KNOW_THIS_WIPES_MY_DISK:-}" ]; then
-    echo "⚠️  WARNING: This script will perform DESTRUCTIVE operations!"
+if [ "${TARGET_ROOT}" != "/mnt/sysroot" ] && [ -z "${BOOTC_CONFIRM_DISK_WIPE:-}" ]; then
+    echo "🚨 CRITICAL SAFETY WARNING 🚨"
+    echo "This script will perform DESTRUCTIVE operations!"
     echo "Target: ${TARGET_ROOT}"
     echo "This may WIPE existing data and partitions!"
     echo ""
-    echo "To proceed, set: BOOTC_I_KNOW_THIS_WIPES_MY_DISK=1"
-    echo "Example: BOOTC_I_KNOW_THIS_WIPES_MY_DISK=1 $0 ${IMAGE_NAME} ${TARGET_ROOT}"
+    echo "THIS IS EXPERIMENTAL SOFTWARE - Expect failures and data loss!"
+    echo ""
+    echo "MANDATORY: Set BOOTC_CONFIRM_DISK_WIPE=1 to proceed"
+    echo "Example: BOOTC_CONFIRM_DISK_WIPE=1 $0 ${IMAGE_NAME} ${TARGET_ROOT}"
+    echo ""
+    echo "Sleeping 10 seconds before exit..."
+    sleep 10
     exit 1
 fi