Phase 2: DataFusion query engine over Parquet

- queryd: SessionContext with custom URL scheme to avoid path doubling with LocalFileSystem
- queryd: ListingTable registration from catalog ObjectRefs with schema inference
- queryd: POST /query/sql returns JSON {columns, rows, row_count}
- queryd→catalogd wiring: reads all datasets, registers as named tables
- gateway: wires QueryEngine with shared store + registry
- e2e verified: SELECT *, WHERE/ORDER BY, COUNT/AVG all correct

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/e2e_query.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# End-to-end test: upload Parquet → register dataset → SQL query
+set -e
+
+BASE="http://localhost:3100"
+
+echo "=== Generate test Parquet file ==="
+python3 -c "
+import struct, io
+
+# Minimal Parquet via pyarrow if available, else skip
+try:
+    import pyarrow as pa
+    import pyarrow.parquet as pq
+    table = pa.table({
+        'id': [1, 2, 3, 4, 5],
+        'name': ['alice', 'bob', 'carol', 'dave', 'eve'],
+        'score': [9.5, 8.2, 7.8, 6.1, 9.9],
+    })
+    pq.write_table(table, '/tmp/test_data.parquet')
+    print('generated with pyarrow')
+except ImportError:
+    print('pyarrow not available, generating via rust helper')
+    exit(1)
+"
+
+echo "=== Upload Parquet to storage ==="
+curl -s -X PUT "$BASE/storage/objects/datasets/scores.parquet" \
+  --data-binary @/tmp/test_data.parquet
+echo ""
+
+echo "=== Register dataset in catalog ==="
+SIZE=$(stat -c%s /tmp/test_data.parquet)
+curl -s -X POST "$BASE/catalog/datasets" \
+  -H "Content-Type: application/json" \
+  -d "{\"name\":\"scores\",\"schema_fingerprint\":\"test\",\"objects\":[{\"bucket\":\"data\",\"key\":\"datasets/scores.parquet\",\"size_bytes\":$SIZE}]}" | python3 -m json.tool
+echo ""
+
+echo "=== SQL: SELECT * FROM scores ==="
+curl -s -X POST "$BASE/query/sql" \
+  -H "Content-Type: application/json" \
+  -d '{"sql":"SELECT * FROM scores"}' | python3 -m json.tool
+echo ""
+
+echo "=== SQL: SELECT name, score FROM scores WHERE score > 8.0 ORDER BY score DESC ==="
+curl -s -X POST "$BASE/query/sql" \
+  -H "Content-Type: application/json" \
+  -d '{"sql":"SELECT name, score FROM scores WHERE score > 8.0 ORDER BY score DESC"}' | python3 -m json.tool
+echo ""
+
+echo "=== SQL: SELECT COUNT(*), AVG(score) FROM scores ==="
+curl -s -X POST "$BASE/query/sql" \
+  -H "Content-Type: application/json" \
+  -d '{"sql":"SELECT COUNT(*) as cnt, AVG(score) as avg_score FROM scores"}' | python3 -m json.tool
+echo ""
+
+echo "=== DONE ==="