refactor: extract config.py, add burn_only, fix title_segments and font size

- Extract all path/API config to config.py (single source of truth)
- Add run.py / burn_only.py / run.bat / burn.bat entry points
- burn_only: skip transcription/subtitle gen, fast reburn existing SRTs
- Fix title_segments: use transcript keyword time for split point
- Fix subtitle: each overlapping title shows max title_duration (not full clip)
- Fix burn_only font size: default from 90 to 60
- Delete old run_lesson1.bat/py, temp debug scripts
- Update README, ARCHITECTURE, CHANGELOG, add USAGE.md

run.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+"""
+完整流水线 - 从 PPT 解析到最终视频输出
+配置统一在 config.py 中管理。
+"""
+import sys
+import os
+import subprocess
+
+# 导入统一配置
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+import config
+
+env = os.environ.copy()
+env["PATH"] = os.path.dirname(config.PYTHON) + ";" + env.get("PATH", "")
+
+cmd = [
+    config.PYTHON,
+    os.path.join(config.CLI_DIR, "src", "cli.py"),
+    "--video", config.VIDEO,
+    "--ppt", config.PPT,
+    "--output", config.OUTPUT,
+    "--api-key", config.API_KEY,
+    "--api-host", config.API_HOST,
+    "--max-total-duration", str(config.MAX_TOTAL_DURATION),
+    "--verbose",
+]
+
+print(f"Running pipeline...")
+print(f"  Video: {config.VIDEO}")
+print(f"  PPT:   {config.PPT}")
+print(f"  Output: {config.OUTPUT}")
+print()
+
+proc = subprocess.Popen(cmd, cwd=config.CLI_DIR, env=env)
+proc.wait()