refactor: align market_events categories with driver types + event stars on chart

- database.py: idempotent migration — calendar→event_calendar, geopolitique→geopolitical,
  macro events classified by name pattern (FOMC/CPI/BOJ/OPEC+→event_calendar,
  NVIDIA→report, rest→fundamental)
- eco_calendar_bootstrap.py: calendar→event_calendar (75 events)
- macro_events_bootstrap.py: all 30 events now carry aligned category + sub_type
  (FOMC×9, CPI×3, BOJ×3, OPEC+×2 → event_calendar ; war/geo×6 → geopolitical ;
   ChatGPT/BTC/PBOC → fundamental ; NVIDIA×2 → report)
- InstrumentDashboard: replace EventTimelineStrip (horizontal bars below chart)
  with EventStarsStrip (★ icons above chart, sized by impact_score, colored by category)

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

backend/services/database.py

@@ -916,6 +916,32 @@ def init_db():
             (_t,)
         )
 
+    # ── Migrate legacy market_events category values to aligned driver types ──
+    # Idempotent: only updates rows that still carry the old values
+    try:
+        # eco events: "calendar" → "event_calendar"
+        c.execute("UPDATE market_events SET category='event_calendar' WHERE category='calendar'")
+        # geo events: "geopolitique" → "geopolitical"
+        c.execute("UPDATE market_events SET category='geopolitical' WHERE category='geopolitique'")
+        # macro events: classify by name prefix and add sub_type
+        for _pattern, _cat, _sub in [
+            ('FOMC%',   'event_calendar', 'FOMC'),
+            ('CPI%',    'event_calendar', 'CPI'),
+            ('BOJ%',    'event_calendar', 'BOJ'),
+            ('OPEP%',   'event_calendar', 'OPEC+'),
+            ('OPEC%',   'event_calendar', 'OPEC+'),
+        ]:
+            c.execute(
+                "UPDATE market_events SET category=?, sub_type=COALESCE(NULLIF(sub_type,''),?) "
+                "WHERE category='macro' AND name LIKE ?",
+                (_cat, _sub, _pattern),
+            )
+        c.execute("UPDATE market_events SET category='report' WHERE category='macro' AND name LIKE 'NVIDIA%'")
+        # remaining macro (ChatGPT, Bitcoin, Stimulus...) → fundamental
+        c.execute("UPDATE market_events SET category='fundamental' WHERE category='macro'")
+    except Exception:
+        pass
+
     conn.commit()
     conn.close()