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.

tests/test_api_heavy_compute_gate.py

@@ -112,6 +112,9 @@ def test_health_and_light_paths_are_not_gated() -> None:
     assert is_heavy_compute_path("/api/rectification/sensitivity_scan")
     assert is_heavy_compute_path("/api/vedastro_gateway/jobs/job1/run")
     assert "/api/chart" not in HEAVY_COMPUTE_PATHS
+    assert is_heavy_compute_path("/api/qizheng")
+    assert is_heavy_compute_path("/api/western")
+    assert is_heavy_compute_path("/api/ephemeris_events")
     assert DEFAULT_CONCURRENCY == 2