feat(agents): stars agent — astrological transits via pyswisseph (#121)

Computes natal chart (Sun/Moon/Mercury/Venus/Mars/Jupiter/Saturn) from
birth_date and finds active transits (conjunction/sextile/square/trine/
opposition) between today's sky and the user's natal positions. Top 3
most-exact transits are passed to the orchestrator as interpretive themes
to colour the tip — grounded and actionable, not predictive.

Birth date sourced from agent_prefs (populated by a connected Google
data source); requires data:google-health consent. Agent self-silences
when birth_date is absent. pyswisseph added to ml/serving/requirements.txt.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ml/agents/registry.py

@@ -18,6 +18,7 @@ from .recent_patterns import RecentPatternsAgent, MANIFEST as RECENT_PATTERNS_MA
 from .focus_area import FocusAreaAgent, MANIFEST as FOCUS_AREA_MANIFEST
 from .health_vitals import HealthVitalsAgent, MANIFEST as HEALTH_VITALS_MANIFEST
 from .tarot import TarotAgent, MANIFEST as TAROT_MANIFEST
+from .stars import StarsAgent, MANIFEST as STARS_MANIFEST
 
 _REGISTERED: list[tuple[BaseAgent, AgentManifest]] = [
     (OverdueTaskAgent(), OVERDUE_TASK_MANIFEST),
@@ -27,6 +28,7 @@ _REGISTERED: list[tuple[BaseAgent, AgentManifest]] = [
     (FocusAreaAgent(), FOCUS_AREA_MANIFEST),
     (HealthVitalsAgent(), HEALTH_VITALS_MANIFEST),
     (TarotAgent(), TAROT_MANIFEST),
+    (StarsAgent(), STARS_MANIFEST),
 ]
 
 # Sanity check — agent_id and manifest.id must agree, otherwise the registry