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>

src/scroll-preview.rs

@@ -0,0 +1,40 @@
+//! Explicit manual scroll preview. Never used as a TV inventory fallback.
+use crate::{i18n::Language, model::Inventory};
+
+const PREFIX: &str = "com.luma.scroll-preview.";
+
+pub fn is_placeholder(id: &str) -> bool {
+    id.starts_with(PREFIX)
+}
+
+pub fn append(inventory: &mut Inventory, count: usize, language: Language) {
+    if count == 0 {
+        return;
+    }
+    let templates = inventory.apps.clone();
+    if templates.is_empty() {
+        eprintln!("Luma scroll preview: no real apps to use as artwork templates");
+        return;
+    }
+    let mut added = 0;
+    for index in 0..count {
+        let id = format!("{PREFIX}{index:03}");
+        if inventory.apps.iter().any(|app| app.id == id) {
+            continue;
+        }
+        let mut app = templates[index % templates.len()].clone();
+        app.id = id;
+        app.title = format!(
+            "{} {:03} · {}",
+            language.t("scrollTestApp"),
+            index + 1,
+            app.title
+        );
+        inventory.apps.push(app);
+        added += 1;
+    }
+    eprintln!(
+        "Luma scroll preview: {added} placeholder apps appended to {} real apps",
+        templates.len()
+    );
+}