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

mkdocs.yml

@@ -283,6 +283,7 @@ nav:
     - Version Generation: toolchain/compile_vergen.md
     - LVGL Compilation: toolchain/compile_lvgl.md
     - Wasuro Pull: toolchain/compile_wasuro.md
+    - Automatic Boot Units: toolchain/dangling_units.md
     - Source List: toolchain/compile_sourcelist.md
     - Source Compilation: toolchain/compile_sources.md
     - Checksum: toolchain/compile_checksum.md