P7.9: fix headless export — resolve Resource class_name ordering + duplicate RoundManager + simulation stub API

- Fix dead code in server_main.gd (unreachable lag compensation print)
- Remove WeaponData type hints from weapon_server.gd (Resource class_name in Node scripts = headless fail)
- Use preload() instead of WeaponData class_name in weapon_definitions.gd for const refs
- Lazy-init WEAPONS dict (const can't reference preload members)
- Remove duplicate class_name RoundManager from server/scripts/round/round_manager.gd
- Remove DamageProcessor type hints from round/round_manager.gd and bomb_objective.gd
- Add start()/stop()/can_tick()/tick()/spawn_entity()/despawn_entity() to simulation_server_stub.gd
- Fix get_world_3d() → get_tree().root.world_3d in weapon_server.gd Node context
- Fix var data := → var data = for untyped WeaponDefinitions.get_weapon() returns
- Clean export cache and verify server starts with zero parse errors

scripts/combat/weapon_definitions.gd

@@ -12,23 +12,38 @@
 extends RefCounted
 class_name WeaponDefinitions
 
+# Preload WeaponData script directly (no class_name dependency — the server
+# weapon_data.gd intentionally avoids class_name to avoid conflicts with
+# client/weapons/data/weapon_data.gd which also registers WeaponData).
+const _WD = preload("res://scripts/combat/weapon_data.gd")
+
 # ---------------------------------------------------------------------------
-# Weapon Registry
+# Weapon Registry — lazily initialised to avoid const + .new() errors
 # ---------------------------------------------------------------------------
 
+## Whether the WEAPONS dictionary has been populated.
+static var _initialized: bool = false
+
 ## All weapons indexed by weapon_id — the single source of truth for the
-## game's starter arsenal. Add new weapons here and in WeaponData.
-const WEAPONS: Dictionary = {
-    "rifle":   WeaponData.RIFLE,
-    "pistol":  WeaponData.PISTOL,
-    "shotgun": WeaponData.SHOTGUN,
-    "smg":     WeaponData.SMG,
-}
+## game's starter arsenal. Populated on first access via _ensure_init().
+static var WEAPONS: Dictionary = {}
+
+static func _ensure_init() -> void:
+	if _initialized:
+		return
+	_initialized = true
+	WEAPONS = {
+		"rifle":   _WD.RIFLE,
+		"pistol":  _WD.PISTOL,
+		"shotgun": _WD.SHOTGUN,
+		"smg":     _WD.SMG,
+	}
 
 # ---------------------------------------------------------------------------
 # Lookup
 # ---------------------------------------------------------------------------
 
 ## Return the WeaponData for the given weapon_id, or null if unknown.
-static func get_weapon(id: String) -> WeaponData:
-    return WEAPONS.get(id, null) as WeaponData
+static func get_weapon(id: String):
+	_ensure_init()
+	return WEAPONS.get(id, null)