Fix Parser Test Runner JSON mode, Filter Simulator PQ syntax, dropdown source

- backend/routers/quality.py
 * Add GET /api/quality/parsers (lists actual files in /app/parsers)
 * Support SDL JSON auto-extract parsers ($=json{parse=json}$)
 * Apply parser rewrite blocks with correct $0/$N backref translation
 * Accept single JSON / JSON array / NDJSON in test-parser body
 * Flatten JSON inside 'message' for Field Population coverage
- backend/routers/ingest.py
 * Rewrite simulate-filter PowerQuery to valid SDL syntax
 * Correct field name: src.name -> dataSource.name
- frontend/index.html
 * Parser dropdown loads from /api/quality/parsers
 * Add 'Last 7d' lookback option
 * Render JSON-mode test results with badges + payload counter

backend/routers/ingest.py

@@ -92,12 +92,15 @@ async def simulate_filter(rule: FilterRule):
 
     clauses = []
     if rule.source:
-        clauses.append(f'src.name = "{rule.source}"')
+        clauses.append(f"dataSource.name=='{rule.source}'")
     if rule.event_type:
-        clauses.append(f'event.type = "{rule.event_type}"')
+        clauses.append(f"event.type=='{rule.event_type}'")
 
-    filter_expr = " AND ".join(clauses) if clauses else "true"
-    query = f"| filter {filter_expr} | count() as events"
+    if clauses:
+        filter_expr = " and ".join(clauses)
+        query = f"| filter {filter_expr} | group events=count()"
+    else:
+        query = "| group events=count()"
 
     try:
         result = await s1_client.run_powerquery(query, from_dt, to_dt)