Fix Chinese font rendering in all chart outputs

- Add src/font_config.py: centralized font detection that auto-selects
  from Noto Sans SC > Hiragino Sans GB > STHeiti > Arial Unicode MS
- Replace hardcoded font lists in all 18 modules with unified config
- Add .gitignore for __pycache__, .DS_Store, venv, etc.
- Regenerate all 70 charts with correct Chinese rendering

Previously, 7 modules (fft, wavelet, acf, fractal, hurst, indicators,
patterns) had no Chinese font config at all, causing □□□ rendering.
The remaining 11 modules used a hardcoded fallback list that didn't
prioritize the best available system font.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/causality.py

@@ -543,9 +543,8 @@ def run_causality_analysis(
     print(f"因果变量对数: {len(CAUSALITY_PAIRS)}")
     print(f"总检验次数（含所有滞后）: {len(CAUSALITY_PAIRS) * len(TEST_LAGS)}")
 
-    # 设置中文字体
-    plt.rcParams['font.sans-serif'] = ['Arial Unicode MS', 'SimHei', 'DejaVu Sans']
-    plt.rcParams['axes.unicode_minus'] = False
+    from src.font_config import configure_chinese_font
+    configure_chinese_font()
 
     # --- 日线级 Granger 因果检验 ---
     print("\n>>> [1/4] 执行日线级 Granger 因果检验...")