fix(release): bump pyproject.toml version to 0.3.1

The previous v0.3.1 commit only bumped `deeptrade/__init__.py`, but
hatchling builds the wheel from the static `version` in pyproject.toml.
The release workflow built a 0.3.0 wheel and PyPI rejected the upload
(file already exists). Tag v0.3.1 will be moved to this commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ty19880929

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "deeptrade-quant"
-version = "0.3.0"
+version = "0.3.1"
 description = "LLM-driven A-share (Shanghai/Shenzhen main board) stock screening CLI"
 readme = "README.md"
 requires-python = ">=3.11"