Complete wallpaper support with new config

Load wallpaper_image_path from config with tilde expansion (environment
variables are not supported)

On the way for this commit, I also had to:
- Fix wallpaper not rendering on startup by triggering init from
the .wl_output handler, since wl_output.done is lost during the
initial roundtrip
- Re-render wallpapers on config reload when the path changes
- Fix crash in deinitWallpaperLayerSurface when wl_surface is null

src/main.zig

@@ -134,6 +134,10 @@ fn registryListener(registry: *wl.Registry, event: wl.Registry.Event, globals: *
     }
 }
 
+pub const std_options = std.Options{
+    .log_level = .debug,
+};
+
 const std = @import("std");
 const mem = std.mem;
 const fatal = std.process.fatal;