fix: retry population on failure, report all table counts, fail loudly if fact tables empty

- After gen.generate(), check all tables for 0 rows
- If anything failed (exception or empty fact table), auto-retry once with truncate_first=True
- Log final row count for every table with pass/fail indicator
- Raise with combined error message if fact tables still empty after 2 attempts

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

legitdata_bridge.py

@@ -567,15 +567,44 @@ def populate_demo_data(
         log(f"Generating {size} dataset...")
         log("   This may take a few minutes...")
         
-        results = gen.generate(size=size, truncate_first=truncate_first)
+        # Attempt 1
+        results = {}
+        first_attempt_error = None
+        try:
+            results = gen.generate(size=size, truncate_first=truncate_first)
+        except RuntimeError as e:
+            first_attempt_error = str(e)
+            log(f"⚠️ First population attempt failed: {first_attempt_error}")
 
-        # Verify fact tables have data — empty fact table = unusable demo
+        # Check all tables for 0 rows even if no exception
         fact_table_names = {t.name for t in schema.fact_tables}
         empty_facts = [t for t in fact_table_names if results.get(t, 0) == 0]
-        if empty_facts:
+        if not first_attempt_error and empty_facts:
+            first_attempt_error = f"Fact table(s) empty after first attempt: {', '.join(empty_facts)}"
+            log(f"⚠️ {first_attempt_error}")
+
+        # Attempt 2 if anything failed
+        if first_attempt_error:
+            log("🔄 Retrying data population (attempt 2 of 2)...")
+            try:
+                results = gen.generate(size=size, truncate_first=True)
+            except RuntimeError as retry_e:
+                raise RuntimeError(
+                    f"Population failed after 2 attempts. "
+                    f"Attempt 1: {first_attempt_error} | Attempt 2: {retry_e}"
+                )
+
+        # Final check — report all table counts and fail if fact tables still empty
+        log("\nFinal table row counts:")
+        for table_name, count in sorted(results.items()):
+            status = "✅" if count > 0 else "❌"
+            log(f"  {status} {table_name}: {count:,} rows")
+
+        empty_facts_final = [t for t in fact_table_names if results.get(t, 0) == 0]
+        if empty_facts_final:
             raise RuntimeError(
-                f"Fact table(s) have 0 rows after population: {', '.join(empty_facts)}. "
-                f"Check insert errors above."
+                f"Fact table(s) still empty after 2 attempts: {', '.join(empty_facts_final)}. "
+                f"First attempt error: {first_attempt_error}"
             )
 
         # Format results