Add Flatpak welcome modal and sequential modal priority system

- Add FlatpakWelcomeModal component shown once for Flatpak users
- Add persistence for Flatpak welcome shown state (updates.db)
- Implement sequential modal priority: Flatpak > What's new > Update available
- Add Flatpak section to Settings navigation (only when running in Flatpak)
- Clean up duplicate Flatpak section and invalid style block in SettingsView
- Add copyable command styling for Flatpak section

src-tauri/src/lib.rs

@@ -771,6 +771,8 @@ pub fn run() {
             updates::is_release_ignored,
             updates::has_whats_new_been_shown,
             updates::mark_whats_new_shown,
+            updates::has_flatpak_welcome_been_shown,
+            updates::mark_flatpak_welcome_shown,
             updates::get_current_version,
             updates::check_for_updates,
             updates::fetch_release_for_version,

src-tauri/src/updates/mod.rs

@@ -123,6 +123,11 @@ impl UpdatesStore {
             CREATE TABLE IF NOT EXISTS whats_new_shown (
                 version TEXT PRIMARY KEY,
                 shown_at INTEGER NOT NULL
+            );
+
+            CREATE TABLE IF NOT EXISTS flatpak_welcome_shown (
+                id INTEGER PRIMARY KEY CHECK (id = 1),
+                shown_at INTEGER NOT NULL
             );",
         )
         .map_err(|e| format!("Failed to create updates tables: {}", e))?;
@@ -233,6 +238,26 @@ impl UpdatesStore {
             .map_err(|e| format!("Failed to mark whats_new_shown: {}", e))?;
         Ok(())
     }
+
+    pub fn has_flatpak_welcome_been_shown(&self) -> bool {
+        self.conn
+            .query_row(
+                "SELECT 1 FROM flatpak_welcome_shown WHERE id = 1 LIMIT 1",
+                [],
+                |_row| Ok(()),
+            )
+            .is_ok()
+    }
+
+    pub fn mark_flatpak_welcome_shown(&self) -> Result<(), String> {
+        self.conn
+            .execute(
+                "INSERT OR REPLACE INTO flatpak_welcome_shown (id, shown_at) VALUES (1, ?1)",
+                params![now_epoch_seconds()],
+            )
+            .map_err(|e| format!("Failed to mark flatpak_welcome_shown: {}", e))?;
+        Ok(())
+    }
 }
 
 /// Thread-safe state wrapper
@@ -448,6 +473,16 @@ pub fn mark_whats_new_shown(version: String, state: tauri::State<UpdatesState>)
     state.with_store(|store| store.mark_whats_new_shown(&version))
 }
 
+#[tauri::command]
+pub fn has_flatpak_welcome_been_shown(state: tauri::State<UpdatesState>) -> bool {
+    state.with_store(|store| store.has_flatpak_welcome_been_shown())
+}
+
+#[tauri::command]
+pub fn mark_flatpak_welcome_shown(state: tauri::State<UpdatesState>) -> Result<(), String> {
+    state.with_store(|store| store.mark_flatpak_welcome_shown())
+}
+
 #[tauri::command]
 pub fn get_current_version(state: tauri::State<UpdatesState>) -> String {
     state.current_version()