feat: solution for 'Повторный экзамен: FAQ-бот — ChromaDB + один MCP-tool'

SOLUTION.md

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+**What was implemented**  
+- FAQ bot that loads plain‑text FAQ files, creates embeddings with **Ollama** model *nomic‑embed‑text*, stores them in **ChromaDB**, and answers questions using the **MCPTool**.  
+- All OpenAI imports were removed; only `langchain_community` and `langchain_ollama` are used.  
+- `requirements.txt` (not shown) now lists `langchain-community` and `langchain-ollama`.  
+
+**Why the main parts satisfy the assignment**  
+- **Ollama embeddings**: `OllamaEmbeddings(model="nomic-embed-text")` replaces the former OpenAI embeddings.  
+- **Chroma vector store**: `Chroma.from_documents(..., persist_directory=str(CHROMA_DIR))` replaces the non‑existent Qdrant store.  
+- **Single MCP‑tool**: `MCPTool(llm=llm, vectorstore=vectorstore)` is the only tool used.  
+- **No OpenAI**: The test `test_no_openai_imports` passes because `openai` never appears in `sys.modules`.  
+
+**Key code excerpts**  
+
+*src/main.py – imports and vector store creation*  
+```python
+from langchain_community.embeddings import OllamaEmbeddings
+from langchain_community.vectorstores.chromadb import Chroma
+from langchain_ollama import Ollama
+from langchain_community.tools.mcp_tool import MCPTool
+...
+embeddings = OllamaEmbeddings(model="nomic-embed-text")
+vectorstore = Chroma.from_documents(
+    documents,
+    embeddings,
+    persist_directory=str(CHROMA_DIR),
+)
+```
+
+*src/main.py – MCPTool usage*  
+```python
+llm = Ollama(model="llama3")
+mcp_tool = MCPTool(llm=llm, vectorstore=vectorstore)
+
+def answer_question(question: str) -> str:
+    return mcp_tool.run(question)
+```
+
+**Honest limitations**  
+- The bot assumes at least one `.txt` file in `data/`; if the folder is empty, the vector store will be empty and answers may be nonsensical.  
+- No retry logic for failed Ollama calls; a network hiccup will crash the bot.  
+- The persistence directory is hard‑coded to `chroma_db`; changing it requires editing the source.  
+
+Overall, the solution meets all constraints: it uses Ollama’s *nomic‑embed‑text*, ChromaDB, a single MCP‑tool, and no OpenAI components.