build: remove testing.sh in favor of runit.sh; add claude.md reference

Replace inline boot testing with standalone runit.sh runner for clarity:
- Remove scripts/lib/testing.sh source and boot_tests stage from build.sh
- Remove --skip-tests option from build.sh and rebuild-after-zinit.sh
- Update all docs to reference runit.sh for QEMU/cloud-hypervisor testing
- Add comprehensive claude.md as AI assistant entry point with guidelines

Testing is now fully decoupled from build pipeline; use ./runit.sh for
QEMU/cloud-hypervisor validation after builds complete.

scripts/rebuild-after-zinit.sh

@@ -218,13 +218,9 @@ build_from_args=()
 
 if in_container; then
   # Run directly when already inside the dev/build container
-  if [[ "$run_tests" -eq 1 ]]; then
-    log "Including boot tests (in-container)"
-    DEBUG=1 "${PROJECT_ROOT}/scripts/build.sh" "${build_from_args[@]}" "${extra_args[@]}"
-  else
-    log "Skipping boot tests (in-container)"
-    DEBUG=1 "${PROJECT_ROOT}/scripts/build.sh" --skip-tests "${build_from_args[@]}" "${extra_args[@]}"
-  fi
+  # Note: Tests are run separately using runit.sh, not during build
+  log "Running rebuild (in-container) - use runit.sh for testing"
+  DEBUG=1 "${PROJECT_ROOT}/scripts/build.sh" "${build_from_args[@]}" "${extra_args[@]}"
 else
   # Not in container: delegate to dev-container manager which ensures container exists and is running
   devctl="${PROJECT_ROOT}/scripts/dev-container.sh"
@@ -234,11 +230,7 @@ else
     exit 1
   fi
 
-  if [[ "$run_tests" -eq 1 ]]; then
-    log "Including boot tests via dev-container"
-    "$devctl" build "${build_from_args[@]}" "${extra_args[@]}"
-  else
-    log "Skipping boot tests via dev-container"
-    "$devctl" build --skip-tests "${build_from_args[@]}" "${extra_args[@]}"
-  fi
+  # Note: Tests are run separately using runit.sh, not during build
+  log "Running rebuild via dev-container - use runit.sh for testing"
+  "$devctl" build "${build_from_args[@]}" "${extra_args[@]}"
 fi