chore: reorganize submodule structure into apps/services hierarchy

- Move fastAPI from root to services/fastapi
- Update README with new structure and confirmed tech stack
- Update pad_scanner pointer to latest (.gitignore fix)
- Add services/fastapi submodule

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "apps/pad_scanner"]
 	path = apps/pad_scanner
-	url = git@gitea.server10086.icu:admin/pad_scanner.git
+	url = git@gitea.server10086.icu:CargoTrace/pad_scanner.git
+[submodule "services/fastapi"]
+	path = services/fastapi
+	url = git@gitea.server10086.icu:CargoTrace/fastAPI.git