fix: align requirements.txt version constraints with pyproject.toml

requirements.txt had no version pins for any dependency, while
pyproject.toml specified minimum versions. This caused users
installing via 'pip install -r requirements.txt' to potentially
get incompatible old versions (e.g., yfinance 0.2.43 which cannot
fetch stock data due to Yahoo Finance API changes).

Added minimum version constraints to all packages matching the
versions specified in pyproject.toml.

Fixes #417

requirements.txt

@@ -1,22 +1,22 @@
-typing-extensions
-langchain-core
-langchain-openai
-langchain-experimental
-pandas
-yfinance
-stockstats
-langgraph
-rank-bm25
-setuptools
-backtrader
-parsel
-requests
-tqdm
-pytz
-redis
-chainlit
-rich
-typer
-questionary
-langchain_anthropic
-langchain-google-genai
+typing-extensions>=4.14.0
+langchain-core>=0.3.81
+langchain-openai>=0.3.23
+langchain-experimental>=0.3.4
+pandas>=2.3.0
+yfinance>=0.2.63
+stockstats>=0.6.5
+langgraph>=0.4.8
+rank-bm25>=0.2.2
+setuptools>=80.9.0
+backtrader>=1.9.78.123
+parsel>=1.10.0
+requests>=2.32.4
+tqdm>=4.67.1
+pytz>=2025.2
+redis>=6.2.0
+chainlit>=2.5.5
+rich>=14.0.0
+typer>=0.21.0
+questionary>=2.1.0
+langchain_anthropic>=0.3.15
+langchain-google-genai>=2.1.5