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/options.rs

@@ -0,0 +1,54 @@
+//! Writes player keybinds / preferences into Minecraft's `options.txt`.
+
+use anyhow::Result;
+use std::collections::BTreeMap;
+use std::path::Path;
+
+/// Merge `key_<binding>:<key>` lines into options.txt, keeping everything
+/// else the game has written. Only for 1.13+ (named key codes).
+pub fn apply_keybinds(game_dir: &Path, binds: &BTreeMap<String, String>) -> Result<()> {
+    let mut values: BTreeMap<String, String> = binds.iter().map(|(k, v)| (format!("key_{k}"), v.clone())).collect();
+    apply(game_dir, &mut values)
+}
+
+/// Merge arbitrary `name:value` options.
+pub fn apply(game_dir: &Path, values: &mut BTreeMap<String, String>) -> Result<()> {
+    if values.is_empty() {
+        return Ok(());
+    }
+    let path = game_dir.join("options.txt");
+    let existing = std::fs::read_to_string(&path).unwrap_or_default();
+    let mut lines: Vec<String> = Vec::new();
+    for line in existing.lines() {
+        match line.split_once(':') {
+            Some((k, _)) if values.contains_key(k) => {
+                let v = values.remove(k).unwrap();
+                lines.push(format!("{k}:{v}"));
+            }
+            _ => lines.push(line.to_string()),
+        }
+    }
+    for (k, v) in values.iter() {
+        lines.push(format!("{k}:{v}"));
+    }
+    std::fs::create_dir_all(game_dir)?;
+    std::fs::write(path, lines.join("\n") + "\n")?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn merges_keybinds() {
+        let dir = tempfile::tempdir().unwrap();
+        std::fs::write(dir.path().join("options.txt"), "version:3465\nkey_key.forward:key.keyboard.w\nfov:0.0\n").unwrap();
+        let mut binds = BTreeMap::new();
+        binds.insert("key.forward".to_string(), "key.keyboard.up".to_string());
+        binds.insert("key.sprint".to_string(), "key.keyboard.left.control".to_string());
+        apply_keybinds(dir.path(), &binds).unwrap();
+        let out = std::fs::read_to_string(dir.path().join("options.txt")).unwrap();
+        assert_eq!(out, "version:3465\nkey_key.forward:key.keyboard.up\nfov:0.0\nkey_key.sprint:key.keyboard.left.control\n");
+    }
+}