Merge Luma launcher fork into monorepo

Move trampoline files (boot-hook, watcher, overlay) into trampoline/
subdirectory. Add upstream Luma v2.3.1 source at repo root with our
additions:

- Page::Ha (4th nav tab) with placeholder empty state
- HA tab config schema and default entity mapping (ha-home/)
- Nav keys renamed: "home" → "start", new "ha" tab between Apps and Settings
- All state.rs/view.rs/main.rs/tests.rs updated for 4-tab navigation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

assets/ui-icons/alert.svg

@@ -0,0 +1 @@
+<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.65" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-circle-alert" xmlns="http://www.w3.org/2000/svg" width="128" height="128" color="#fff"><circle cx="12" cy="12" r="10"></circle><line x1="12" x2="12" y1="8" y2="12"></line><line x1="12" x2="12.01" y1="16" y2="16"></line></svg>