Add launcher engine (scopenet-core) and admin panel server

- scopenet-shared: wire types for branding, auth, instances, manifests
- scopenet-core: Mojang versions/libraries/assets, automatic Java runtimes,
  Fabric/Quilt/Forge/NeoForge installation, file sync, launch command
  builder, Microsoft auth, servers.dat injection, server list ping
- scopenet-panel: Axum + SQLite admin API with JWT auth, users/groups,
  branding, settings, instances, Modrinth/CurseForge/zip import, file
  hosting and launch stats

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

crates/core/src/progress.rs

@@ -0,0 +1,33 @@
+use serde::Serialize;
+use std::sync::Arc;
+
+#[derive(Debug, Clone, Copy, Serialize, PartialEq, Eq)]
+#[serde(rename_all = "snake_case")]
+pub enum Stage {
+    Preparing,
+    Java,
+    Game,
+    Loader,
+    Files,
+    Launching,
+}
+
+#[derive(Debug, Clone, Serialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum Event {
+    Stage { stage: Stage, label: String },
+    Progress { stage: Stage, done: u64, total: u64, files_done: u32, files_total: u32 },
+    Log { line: String },
+}
+
+/// Callback the engine uses to report progress. Must be cheap: it is called
+/// from download tasks (throttled to ~10 Hz).
+pub type Reporter = Arc<dyn Fn(Event) + Send + Sync>;
+
+pub fn noop() -> Reporter {
+    Arc::new(|_| {})
+}
+
+pub fn stage(r: &Reporter, stage: Stage, label: impl Into<String>) {
+    r(Event::Stage { stage, label: label.into() });
+}