Add Tauri launcher with Svelte UI

- Accounts: panel login/sign-up, Microsoft device-code sign-in, offline
  play; tokens encrypted with a key kept in the OS credential store
- Home: instance rail, live server status, news feed, social links,
  Play button with download progress, speed and ETA
- Full settings: accounts, memory/resolution/after-launch behaviour,
  Java and GC presets, Minecraft keybind editor applied to options.txt,
  theme overrides, storage manager, self-update via GitHub releases
- Game console, crash dialog with hints, per-instance overrides
- Live admin branding (colours, fonts, backgrounds, custom CSS)
- Online install tests for vanilla/Fabric/Quilt/Forge/NeoForge (CI)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

launcher/src-tauri/src/updater.rs

@@ -0,0 +1,93 @@
+//! Self-update via GitHub Releases: find a newer `*-setup.exe`, download
+//! it and hand over to the installer.
+
+use crate::state::build;
+use anyhow::{anyhow, Context, Result};
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize)]
+pub struct UpdateInfo {
+    pub version: String,
+    pub notes: String,
+    pub url: String,
+    pub size: u64,
+}
+
+#[derive(Deserialize)]
+struct Release {
+    tag_name: String,
+    #[serde(default)]
+    body: String,
+    #[serde(default)]
+    draft: bool,
+    #[serde(default)]
+    prerelease: bool,
+    assets: Vec<Asset>,
+}
+
+#[derive(Deserialize)]
+struct Asset {
+    name: String,
+    browser_download_url: String,
+    size: u64,
+}
+
+fn parse(v: &str) -> Vec<u64> {
+    v.trim_start_matches('v').split(['.', '-', '+']).map_while(|p| p.parse().ok()).collect()
+}
+
+pub fn is_newer(candidate: &str, current: &str) -> bool {
+    parse(candidate) > parse(current)
+}
+
+pub async fn check(http: &reqwest::Client) -> Result<Option<UpdateInfo>> {
+    let Some(repo) = build::REPO.filter(|r| !r.is_empty()) else { return Ok(None) };
+    let release: Release = http
+        .get(format!("https://api.github.com/repos/{repo}/releases/latest"))
+        .header("Accept", "application/vnd.github+json")
+        .send()
+        .await?
+        .error_for_status()?
+        .json()
+        .await?;
+    if release.draft || release.prerelease || !is_newer(&release.tag_name, env!("CARGO_PKG_VERSION")) {
+        return Ok(None);
+    }
+    let asset = release
+        .assets
+        .iter()
+        .find(|a| a.name.to_lowercase().ends_with("-setup.exe"))
+        .ok_or_else(|| anyhow!("release {} has no installer", release.tag_name))?;
+    Ok(Some(UpdateInfo {
+        version: release.tag_name.trim_start_matches('v').to_string(),
+        notes: release.body,
+        url: asset.browser_download_url.clone(),
+        size: asset.size,
+    }))
+}
+
+/// Download the installer and start it. The caller exits the app afterwards.
+pub async fn download_and_run(http: &reqwest::Client, url: &str) -> Result<()> {
+    if !url.starts_with("https://github.com/") && !url.starts_with("https://objects.githubusercontent.com/") {
+        anyhow::bail!("refusing to download an update from an unexpected host");
+    }
+    let dest = std::env::temp_dir().join("scopenet-launcher-setup.exe");
+    let dl = scopenet_core::http::Download::new(url, dest.clone(), None, None);
+    scopenet_core::http::download_one(http, &dl, &|_| {}).await.context("downloading update")?;
+    // /P = passive (progress only), /R = relaunch when done (Tauri NSIS).
+    std::process::Command::new(&dest).args(["/P", "/R"]).spawn().context("starting the installer")?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn versions() {
+        assert!(is_newer("v0.2.0", "0.1.9"));
+        assert!(is_newer("1.0.0", "0.9.12"));
+        assert!(!is_newer("v0.1.0", "0.1.0"));
+        assert!(!is_newer("0.1.0-beta", "0.1.0"));
+    }
+}