perf: index filename candidates and avoid full-corpus retrieval scans

crates/searchi-core/benchmarks/results/windows-cpu-small-optimized.json

@@ -0,0 +1,47 @@
+{
+  "fixture": "synthetic SQLite metadata and text; no filesystem extraction or semantic inference",
+  "files": 10000,
+  "documents": 1000,
+  "seed_seconds": 0.0,
+  "migration_seconds": 0.2795255,
+  "fixture_reused": true,
+  "database_bytes": 6320128,
+  "database_path": "target/benchmarks/small.db",
+  "architecture": "x86_64",
+  "os": "windows",
+  "cpu_only": true,
+  "queries": [
+    {
+      "query": "invoice_0009999.txt",
+      "samples": 20,
+      "p50_ms": 1.9414,
+      "p95_ms": 2.3285,
+      "target_p95_ms": 50.0,
+      "target_met": true
+    },
+    {
+      "query": "invoice_",
+      "samples": 20,
+      "p50_ms": 0.3281,
+      "p95_ms": 1.2427,
+      "target_p95_ms": 50.0,
+      "target_met": true
+    },
+    {
+      "query": "marker0000999",
+      "samples": 20,
+      "p50_ms": 0.2561,
+      "p95_ms": 0.40259999999999996,
+      "target_p95_ms": 150.0,
+      "target_met": true
+    },
+    {
+      "query": "cancellation",
+      "samples": 20,
+      "p50_ms": 1.2418,
+      "p95_ms": 1.7393,
+      "target_p95_ms": 150.0,
+      "target_met": true
+    }
+  ]
+}