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).

installation.md

@@ -1,14 +1,15 @@
 # Installation
 
-⚠️ **CRITICAL SAFETY WARNING** ⚠️
+🚨 **CRITICAL SAFETY WARNING** 🚨
 
 **bootc installation involves DESTRUCTIVE operations that can WIPE your disk and data!**
 
 - `bootc install to-disk` will **DESTROY** existing partitions and data
 - `grub-install` operations can **CORRUPT** your bootloader
+- **THIS IS EXPERIMENTAL SOFTWARE** - Expect failures and data loss
 - Always test on a **virtual machine** or **test hardware** first
 - Never run on production systems without proper backups
-- Use `BOOTC_I_KNOW_THIS_WIPES_MY_DISK=1` environment variable to confirm you understand the risks
+- **MANDATORY**: Use `BOOTC_CONFIRM_DISK_WIPE=1` environment variable to confirm you understand the risks
 
 ## Base Images