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/assets.rs

@@ -0,0 +1,83 @@
+//! Game assets (sounds, languages, textures) — content-addressed objects.
+
+use crate::http::{self, Download};
+use crate::paths::Layout;
+use crate::version::AssetIndexRef;
+use anyhow::Result;
+use serde::Deserialize;
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+
+pub const RESOURCES: &str = "https://resources.download.minecraft.net";
+
+#[derive(Debug, Deserialize)]
+pub struct AssetIndex {
+    pub objects: HashMap<String, AssetObject>,
+    #[serde(default)]
+    pub map_to_resources: bool,
+    #[serde(default, rename = "virtual")]
+    pub is_virtual: bool,
+}
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct AssetObject {
+    pub hash: String,
+    pub size: u64,
+}
+
+pub fn object_path(layout: &Layout, hash: &str) -> PathBuf {
+    layout.assets().join("objects").join(&hash[..2]).join(hash)
+}
+
+/// Load (downloading if needed) the asset index.
+pub async fn load_index(client: &reqwest::Client, layout: &Layout, index: &AssetIndexRef) -> Result<AssetIndex> {
+    let path = layout.assets().join("indexes").join(format!("{}.json", index.id));
+    if !http::file_ok(&path, index.sha1.as_deref(), index.size, true) {
+        http::download_one(client, &Download::new(index.url.clone(), path.clone(), index.sha1.clone(), index.size), &|_| {})
+            .await?;
+    }
+    Ok(serde_json::from_slice(&std::fs::read(&path)?)?)
+}
+
+/// Downloads needed for missing/corrupt objects.
+pub fn missing_objects(layout: &Layout, index: &AssetIndex, deep: bool) -> Vec<Download> {
+    let mut seen = std::collections::HashSet::new();
+    index
+        .objects
+        .values()
+        .filter(|o| o.hash.len() > 2 && seen.insert(o.hash.clone()))
+        .filter_map(|o| {
+            let path = object_path(layout, &o.hash);
+            if http::file_ok(&path, Some(&o.hash), Some(o.size), deep) {
+                None
+            } else {
+                Some(Download::new(format!("{RESOURCES}/{}/{}", &o.hash[..2], o.hash), path, Some(o.hash.clone()), Some(o.size)))
+            }
+        })
+        .collect()
+}
+
+/// Pre-1.7 versions read assets by name, not hash. Copy them into the
+/// virtual (or `resources/`) directory. Returns the directory to pass as
+/// `game_assets`.
+pub fn materialize_legacy(layout: &Layout, index_id: &str, index: &AssetIndex, game_dir: &Path) -> Result<Option<PathBuf>> {
+    if !index.is_virtual && !index.map_to_resources {
+        return Ok(None);
+    }
+    let target = if index.map_to_resources {
+        game_dir.join("resources")
+    } else {
+        layout.assets().join("virtual").join(index_id)
+    };
+    for (name, obj) in &index.objects {
+        let Some(dest) = crate::paths::safe_join(&target, name) else { continue };
+        if dest.exists() {
+            continue;
+        }
+        if let Some(parent) = dest.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        std::fs::copy(object_path(layout, &obj.hash), &dest).ok();
+    }
+    Ok(Some(target))
+}