Automate boot unit inclusion with architecture-aware Moderne analysis

- Replace boot.mgr's static unit list with generated dangling_units.inc
- Generate Pascal LSTs and run the dangling-unit recipe before compilation
- Exclude Wasuro, inactive architectures, and NOT_DANGLING units
- Add ASURO_ARCH selection with an x86 default
- Mark unfinished legacy units as NOT_DANGLING
- Inherit pinned Moderne tooling in the builder image
- Ensure Drone pulls the latest builder image
- Document the updated build pipeline in MkDocs

Validation:
- Full x86 ISO build and VirtualBox boot succeeded
- 1,133 kernel tests passed with no failures
- x86_64 build failed clearly due to unavailable sources

toolchain/architecture.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+# Shared source-architecture selection; callers run from the repository root.
+# Folder names: x86 = i386, x86_64 = x86_64.
+export ASURO_ARCH="${ASURO_ARCH:-x86}"
+if [[ ! "$ASURO_ARCH" =~ ^[a-z][a-z0-9_]*$ ]]; then
+    echo "Invalid ASURO_ARCH: $ASURO_ARCH" >&2
+    return 1
+fi
+if [[ ! -d "src/arch/$ASURO_ARCH" ]]; then
+    echo "Architecture sources not found: src/arch/$ASURO_ARCH" >&2
+    return 1
+fi