chore: manage env with uv (pyproject + lockfile)

Migrate dependency management from requirements.txt to uv. Runtime deps
move to pyproject.toml with pytest in the dev group; uv.lock pins the
resolved set. Docs updated to use `uv sync` / `uv run`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -0,0 +1,22 @@
+[project]
+name = "chinese-equity-quant"
+version = "0.1.0"
+description = "A modular Chinese A-share quant research framework (daily frequency)."
+requires-python = ">=3.10"
+dependencies = [
+    "backtrader>=1.9.76.123",
+    "akshare>=1.14.0",
+    "baostock>=0.8.8",
+    "pandas>=2.0.0",
+    "matplotlib>=3.7.0",
+    "click>=8.0.0",
+    "pyarrow>=14.0.0",
+]
+
+[dependency-groups]
+dev = [
+    "pytest>=7.0.0",
+]
+
+[tool.uv]
+package = false