Add unlabelled event detection, stub parser quality, Sync All, and modern UI redesign

Key changes:
- Unlabelled event banner: shows count only after Sample Events is clicked; uses broad SDL filter expression; time window synced to sync-days dropdown
- Parser Quality: new "Attributes Missing" subsection listing all parsers without dataSource.name regardless of event volume
- Coverage map: filter buttons (All / Complete Parser / Attributes Missing); stat card renamed to "Incomplete Parser"; stub count excluded from sync when no active sources
- Sync All button: runs SDL parser sync → library sync → live sources sync in sequence
- Reset now clears ActiveSource table and resets unlabelled count cache
- run_powerquery: configurable max_count param (default 1000, 50M for count queries)
- _DS_NAME_RE: supports both quoted and unquoted dataSource.name keys in parser files
- Full modern UI redesign: slate palette, gradient cards, ring borders, pill nav, colored stat accents
- Updated 7 tracked parser files synced from SDL

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

backend/db.py

@@ -1,5 +1,5 @@
 import os
-from sqlalchemy import create_engine, Column, Integer, String, Float, DateTime, Text
+from sqlalchemy import create_engine, Column, Integer, String, Float, DateTime, Text, Boolean
 from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import declarative_base, sessionmaker
 from datetime import datetime
@@ -37,6 +37,7 @@ class ActiveSource(Base):
     event_count = Column(Integer, default=0)
     synced_at = Column(DateTime, default=datetime.utcnow)
     parser_detected = Column(Integer, default=0)  # >0 means parsed events seen in data lake
+    unlabelled = Column(Boolean, default=False)   # True = events had no dataSource.name
 
 
 class IngestSnapshot(Base):