Hardened app startup against unrelated broken packages in the user's site-packages: the text-splitter registry now imports the three splitters it uses directly from their `langchain_text_splitters` submodules instead of the package root, whose `__init__` eagerly imports every optional splitter backend (spacy, nltk, konlpy, ...). Previously, a globally installed spacy paired with an incompatible typer/click combination crashed `ldr-web` at startup with `TypeError: type 'Choice' is not subscriptable`.
