Use standard "assets" dir for FAPPs

scripts/fbt/appmanifest.py

@@ -380,7 +380,7 @@ class ApplicationsCGenerator:
             return f"""
     {{.app = NULL,
      .name = "{app.name}",
-     .appid = "/ext/apps/.Main/{app.appid}.fap",
+     .appid = "/ext/apps/assets/{app.appid}.fap",
      .stack_size = 0,
      .icon = {f"&{app.icon}" if app.icon else "NULL"},
      .flags = {'|'.join(f"FlipperInternalApplicationFlag{flag}" for flag in app.flags)}}}"""

scripts/fbt_tools/fbt_extapps.py

@@ -179,7 +179,7 @@ class AppBuilder:
                         deployable = False
                 app_artifacts.dist_entries.append((deployable, fal_path))
         else:
-            fap_path = f"apps/{'.Main' if self.app.apptype == FlipperAppType.FAPP else self.app.fap_category}/{app_artifacts.compact.name}"
+            fap_path = f"apps/{'assets' if self.app.apptype == FlipperAppType.FAPP else self.app.fap_category}/{app_artifacts.compact.name}"
             app_artifacts.dist_entries.append(
                 (self.app.is_default_deployable, fap_path)
             )