feat(qizheng): vendor stem-branch and expose three read-only chart APIs

Add Apache-2.0 @4n6h4x0r/stem-branch 0.8.0, a seven-governors adapter,
and POST /api/qizheng, /api/western, /api/ephemeris_events.

BUG-700 remains blocked (do not call --pillars). BUG-701 and BUG-702 are
resolved. BUG-703 is investigating (panchanga Lahiri). Skill is not bumped.

scripts/api_heavy_compute_gate.py

@@ -36,6 +36,9 @@ HEAVY_COMPUTE_PATHS = frozenset(
         "/api/vedastro/range_scan",
         "/api/vedastro_gateway/run",
         "/api/thematic_report",
+        "/api/qizheng",
+        "/api/western",
+        "/api/ephemeris_events",
     }
 )