fix: use absolute paths in Arma 3 launch args to survive cwd change

Arma 3 changes its own working directory to the exe folder on startup,
so relative paths like -config=server.cfg resolved against A3Master/
instead of the server data dir. Configs were never found, and profile/
battleye dirs pointed at the wrong location (confirmed via RPT location
in A3Master/server/ instead of the data dir).

build_launch_args() now accepts an optional server_dir: Path argument.
When provided, all four path args (-config, -cfg, -profiles, -bepath)
use absolute paths. Service passes server_dir at the call site.

backend/adapters/arma3/config_generator.py

@@ -401,20 +401,36 @@ class Arma3ConfigGenerator:
         self,
         config_sections: dict[str, dict],
         mod_args: list[str] | None = None,
+        server_dir: Path | None = None,
     ) -> list[str]:
         from adapters.exceptions import LaunchArgsError
         launch = LaunchConfig(**config_sections.get("launch", {}))
         server = ServerConfig(**config_sections.get("server", {}))
 
+        # Arma 3 changes its own cwd to the exe directory at startup, so relative
+        # paths in launch args resolve against the exe dir, not server_dir.
+        # Use absolute paths when server_dir is provided so configs are always found.
+        if server_dir is not None:
+            d = Path(server_dir)
+            config_arg   = f"-config={d / 'server.cfg'}"
+            cfg_arg      = f"-cfg={d / 'basic.cfg'}"
+            profiles_arg = f"-profiles={d / 'server'}"
+            bepath_arg   = f"-bepath={d / 'battleye'}"
+        else:
+            config_arg   = "-config=server.cfg"
+            cfg_arg      = "-cfg=basic.cfg"
+            profiles_arg = "-profiles=./server"
+            bepath_arg   = "-bepath=./battleye"
+
         args = [
             f"-port={config_sections.get('_port', 2302)}",
-            "-config=server.cfg",
+            config_arg,
-            "-cfg=basic.cfg",
+            cfg_arg,
-            "-profiles=./server",
+            profiles_arg,
             "-name=server",
             f"-world={launch.world}",
             f"-limitFPS={launch.limit_fps}",
-            "-bepath=./battleye",
+            bepath_arg,
         ]
         if launch.auto_init:
             args.append("-autoInit")

backend/core/servers/service.py

@@ -274,7 +274,7 @@ class ServerService:
 
         # Build launch args
         try:
-            launch_args = config_gen.build_launch_args(raw_sections, mod_args)
+            launch_args = config_gen.build_launch_args(raw_sections, mod_args, server_dir=server_dir)
         except LaunchArgsError as e:
             raise HTTPException(
                 status_code=status.HTTP_400_BAD_REQUEST,