ODIAN Launcher: hub, installer, local stack and remembered sign-in (M2)

- Tauri 2 + Svelte 5 hub in ODIAN dark: patch notes and roadmap, install and
  update progress, local stack status, settings with DHP and MCP addresses.
- crates/odian-packs: Rust installer for pack format v1 (signed manifests,
  resumable verified downloads from a DHP or an ODIAN drive), byte-compatible
  with ODIAN_MCP_Server's Python odian_packs.
- Local stack on 127.0.0.1: Postgres -> Engine API -> tile server -> Odian.exe,
  one Job Object, clean shutdown; database snapshot restore on a fresh PC only.
- Keycloak sign-in through the DHP's MCP, remembered until Sign out with a
  launcher session that renews the Engine token silently.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src-tauri/src/settings.rs

@@ -0,0 +1,98 @@
+//! Launcher settings: which site to use and where ODIAN is installed.
+//!
+//! Stored per Windows user in the launcher's config dir. On first run they are
+//! seeded from a `site.json` next to the launcher executable (shipped with the
+//! setup or copied from an ODIAN drive), so operators never type addresses.
+
+use std::path::{Path, PathBuf};
+
+use serde::{Deserialize, Serialize};
+use tauri::{AppHandle, Manager};
+
+use crate::fsutil::write_json_atomic;
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+pub struct Settings {
+  /// The site's update service, e.g. `http://192.168.1.41:30097`.
+  #[serde(default)]
+  pub site_url: String,
+  /// The site's MCP, which runs the Keycloak sign-in.
+  #[serde(default)]
+  pub mcp_url: String,
+  #[serde(default)]
+  pub install_dir: String,
+  /// Display name from site.json; the UI's settings form does not edit it.
+  #[serde(default, skip_serializing_if = "Option::is_none")]
+  pub site_name: Option<String>,
+}
+
+#[derive(Deserialize, Default)]
+struct SiteFile {
+  #[serde(default)]
+  name: Option<String>,
+  #[serde(default)]
+  site_url: String,
+  #[serde(default)]
+  mcp_url: String,
+}
+
+fn settings_path(app: &AppHandle) -> Result<PathBuf, String> {
+  let dir = app.path().app_config_dir().map_err(|e| format!("no config dir: {e}"))?;
+  Ok(dir.join("settings.json"))
+}
+
+fn default_install_dir() -> String {
+  // Operator PCs keep the ~1 TB of data off the system drive when a D: exists.
+  // Not %LOCALAPPDATA%\ODIAN: on the release PC that folder holds the release
+  // signing key, and deleting a test install must never be able to take it along.
+  if Path::new("D:\\").is_dir() {
+    "D:\\ODIAN".to_string()
+  } else {
+    "C:\\ODIAN".to_string()
+  }
+}
+
+fn read_site_file() -> SiteFile {
+  let Some(dir) = std::env::current_exe().ok().and_then(|exe| exe.parent().map(Path::to_path_buf)) else {
+    return SiteFile::default();
+  };
+  std::fs::read(dir.join("site.json"))
+    .ok()
+    .and_then(|bytes| serde_json::from_slice(&bytes).ok())
+    .unwrap_or_default()
+}
+
+pub fn normalize_url(url: &str) -> String {
+  url.trim().trim_end_matches('/').to_string()
+}
+
+impl Settings {
+  pub fn load(app: &AppHandle) -> Result<Settings, String> {
+    let path = settings_path(app)?;
+    if let Ok(bytes) = std::fs::read(&path) {
+      let mut settings: Settings =
+        serde_json::from_slice(&bytes).map_err(|e| format!("{} is not valid settings JSON: {e}", path.display()))?;
+      if settings.install_dir.trim().is_empty() {
+        settings.install_dir = default_install_dir();
+      }
+      return Ok(settings);
+    }
+    let site = read_site_file();
+    let settings = Settings {
+      site_url: normalize_url(&site.site_url),
+      mcp_url: normalize_url(&site.mcp_url),
+      install_dir: default_install_dir(),
+      site_name: site.name,
+    };
+    settings.save(app)?;
+    Ok(settings)
+  }
+
+  pub fn save(&self, app: &AppHandle) -> Result<(), String> {
+    write_json_atomic(&settings_path(app)?, self)
+  }
+
+  pub fn install_path(&self) -> PathBuf {
+    PathBuf::from(&self.install_dir)
+  }
+}