feat(chart): 「那一刻的天空」封面 — engine, BFF, canvas painter, chart header entry

T1 scripts/birth_sky.py: real alt/az of the seven visible grahas (swe.calc_ut +
swe.azalt, geometric altitude, azimuth converted from swe's south origin to
north-east) and Yale BSC5 stars V<=4.0 (IAU 1976 precession); phase
day / twilight_morning / twilight_evening / night. Thin POST /api/birth_sky
registration in do_POST (no new handler method, no __new__).

T2 GET /api/birth-sky?subject=: birth truth read server side through
loadSubjectBirth + prepareChartViewProfile; zod contract; no billing, no
writes, no birth data in the response.

T3/T4 lib/birth-sky: sentence table, pure Canvas 2D drawBirthSky (night /
paper palettes from DESIGN tokens, east on the left, serif headline with
1.5 s font wait), PNG export via navigator.share or Blob + a.download.
Chart page prefetches and paints the cover once the chart is ok; the header
button appears only when the PNG is ready. Dialog is a lazy chunk.

T7 DESIGN §17, VOICE, CONTEXT glossary, CHANGELOG, real-device checklist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0199rbQDTsUbCVw84wc8BTFe

scripts/run_quality_gate.py

@@ -85,6 +85,8 @@ CORE_PYTEST_TARGETS = [
     "tests/test_qizheng_api_productization.py",
     "tests/test_readonly_chart_endpoints.py",
     "tests/test_ephemeris_events.py",
+    # Birth-sky cover: real alt/az of planets and bright stars (TASK-birth-sky-cover).
+    "tests/test_birth_sky.py",
     # Fail-fast heavy-compute concurrency gate (429 + Retry-After, health ungated).
     "tests/test_api_heavy_compute_gate.py",
     # Upstream-sync acceptance regressions must fail the automatic staging gate.