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/servers_dat.rs

@@ -0,0 +1,84 @@
+//! Adds the instance's server to Minecraft's multiplayer list.
+
+use anyhow::Result;
+use fastnbt::Value;
+use std::collections::HashMap;
+use std::path::Path;
+
+/// Insert (or update) `name`/`address` at the top of `servers.dat`,
+/// preserving every other entry the player has added.
+pub fn upsert(game_dir: &Path, name: &str, address: &str) -> Result<()> {
+    let path = game_dir.join("servers.dat");
+    let mut root: HashMap<String, Value> = match std::fs::read(&path) {
+        Ok(bytes) => match fastnbt::from_bytes::<Value>(&bytes) {
+            Ok(Value::Compound(map)) => map,
+            _ => HashMap::new(),
+        },
+        Err(_) => HashMap::new(),
+    };
+
+    let mut servers = match root.remove("servers") {
+        Some(Value::List(list)) => list,
+        _ => Vec::new(),
+    };
+
+    let same = |v: &Value| match v {
+        Value::Compound(m) => matches!(m.get("ip"), Some(Value::String(ip)) if ip.eq_ignore_ascii_case(address)),
+        _ => false,
+    };
+    let existing = servers.iter().position(same);
+    let mut entry = match existing {
+        Some(i) => match servers.remove(i) {
+            Value::Compound(m) => m,
+            _ => HashMap::new(),
+        },
+        None => HashMap::new(),
+    };
+    entry.insert("name".into(), Value::String(name.to_string()));
+    entry.insert("ip".into(), Value::String(address.to_string()));
+    entry.entry("acceptTextures".into()).or_insert(Value::Byte(1));
+    servers.insert(0, Value::Compound(entry));
+
+    root.insert("servers".into(), Value::List(servers));
+    std::fs::create_dir_all(game_dir)?;
+    std::fs::write(&path, fastnbt::to_bytes(&Value::Compound(root))?)?;
+    Ok(())
+}
+
+pub fn format_address(host: &str, port: u16) -> String {
+    if port == 25565 { host.to_string() } else { format!("{host}:{port}") }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn names(dir: &Path) -> Vec<(String, String)> {
+        let v: Value = fastnbt::from_bytes(&std::fs::read(dir.join("servers.dat")).unwrap()).unwrap();
+        let Value::Compound(root) = v else { panic!() };
+        let Some(Value::List(list)) = root.get("servers") else { panic!() };
+        list.iter()
+            .map(|s| match s {
+                Value::Compound(m) => match (m.get("name"), m.get("ip")) {
+                    (Some(Value::String(n)), Some(Value::String(i))) => (n.clone(), i.clone()),
+                    _ => panic!(),
+                },
+                _ => panic!(),
+            })
+            .collect()
+    }
+
+    #[test]
+    fn upserts_without_losing_player_servers() {
+        let dir = tempfile::tempdir().unwrap();
+        upsert(dir.path(), "Friend", "friend.net").unwrap();
+        upsert(dir.path(), "ScopeNet", "play.scopenet.gg").unwrap();
+        upsert(dir.path(), "ScopeNet SMP", "play.scopenet.gg").unwrap();
+        assert_eq!(
+            names(dir.path()),
+            vec![("ScopeNet SMP".into(), "play.scopenet.gg".into()), ("Friend".into(), "friend.net".into())]
+        );
+        assert_eq!(format_address("a.b", 25565), "a.b");
+        assert_eq!(format_address("a.b", 25570), "a.b:25570");
+    }
+}