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/app-icon.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128">
+  <defs>
+    <linearGradient id="light" x1="61" y1="24" x2="33" y2="93" gradientUnits="userSpaceOnUse">
+      <stop stop-color="#d7fbff"/>
+      <stop offset=".45" stop-color="#80d9f6"/>
+      <stop offset="1" stop-color="#5d73db"/>
+    </linearGradient>
+    <linearGradient id="fold" x1="34" y1="79" x2="99" y2="100" gradientUnits="userSpaceOnUse">
+      <stop stop-color="#8cf0e6"/>
+      <stop offset=".5" stop-color="#48bce5"/>
+      <stop offset="1" stop-color="#7371ec"/>
+    </linearGradient>
+  </defs>
+  <path d="M51 24h21L53 75a4 4 0 0 0 4 5h43l-7 20H45C30 100 22 88 27 74l15-41a14 14 0 0 1 9-9Z" fill="url(#light)"/>
+  <path d="M53 75a4 4 0 0 0 4 5h43l-7 20H45c-9 0-16-4-18-10Z" fill="url(#fold)"/>
+</svg>