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/logos/channel-4.svg

@@ -0,0 +1,2 @@
+<!-- Source: https://raw.githubusercontent.com/simple-icons/simple-icons/90bd1f3e7b77851fd0c56474f6fa43b816babdab/icons/channel4.svg -->
+<svg role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title>Channel 4</title><path d="m14.309 0-.33.412v4.201l2.382-2.95zm-1.155 1.201L10.707 4.22v8.674h2.447zm3.268 1.701-2.443 3.02v14.81h2.443zM9.887 5.236l-6.201 7.657h3.142L9.887 9.12Zm-6.766 8.48v2.444h10.033v-2.443Zm14.125 0v2.444h3.633v-2.443Zm-6.539 3.268V24h2.443v-7.016Zm-3.271 4.573V24h2.443v-2.443zm6.543 0V24h5.189v-2.443z"/></svg>