`StateFileSearchMiddleware`: `grep_search` and `glob_search` return no results when `path` ends in a slash

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [x] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs The `grep_search` behavior is a regression from #39681 (which closed #39679). The `glob_search` behavior predates it. ### Reproduction Steps / Example Code (Python) ```python from langchain_anthropic.middleware.file_search import StateFileSearchMiddleware middleware = StateFileSearchMiddleware() state = { middleware.state_key: { "/app/config.txt": {"content": ["service=web"], "modified_at": 1}, } } for path in ("/app", "/app/"): grep = middleware._handle_grep_search( pattern="service", path=path, include=None, output_mode="files_with_matches", state=state, ) glob = middleware._handle_glob_search(pattern="*.txt", path=path, state=state) print(f"path={path!r:8} grep -> {grep!r:20} glob -> {glob!r}") # path='/app' grep -> '/app/config.txt' glob -> '/a…