perf: optimize HTTP client, DB queries, and clean up dead code

- Make reqwest::Client a LazyLock singleton instead of per-call allocation
- Parallelize 3 independent DB queries in get_index_advisor_report with tokio::join!
- Eliminate per-iteration Vec allocation in snapshot FK dependency loop
- Hoist try_local_pg_dump() call in SampleData clone mode to avoid double execution
- Evict stale schema cache entries on write to prevent unbounded memory growth
- Remove unused ValidationReport struct and config_path field
- Rename IndexRecommendationType variants to remove redundant suffix

src-tauri/src/models/ai.rs

@@ -83,16 +83,6 @@ pub struct ValidationRule {
     pub error: Option<String>,
 }
 
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct ValidationReport {
-    pub rules: Vec<ValidationRule>,
-    pub total_rules: usize,
-    pub passed: usize,
-    pub failed: usize,
-    pub errors: usize,
-    pub execution_time_ms: u128,
-}
-
 // --- Wave 2: Data Generator ---
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -165,9 +155,12 @@ pub struct SlowQuery {
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
 pub enum IndexRecommendationType {
-    CreateIndex,
-    DropIndex,
-    ReplaceIndex,
+    #[serde(rename = "create_index")]
+    Create,
+    #[serde(rename = "drop_index")]
+    Drop,
+    #[serde(rename = "replace_index")]
+    Replace,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]