feat: add cross-database entity lookup for searching column values across all databases

Enables searching for a specific column value (e.g. carrier_id=123) across all databases on a PostgreSQL server. The backend creates temporary connection pools per database (semaphore-limited to 5), queries information_schema for matching columns, and executes read-only SELECTs with real-time progress events. Results are grouped by database/table in a new "Entity Lookup" tab.

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

src-tauri/src/models/lookup.rs

@@ -0,0 +1,44 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LookupTableMatch {
+    pub schema: String,
+    pub table: String,
+    pub column_type: String,
+    pub columns: Vec<String>,
+    pub types: Vec<String>,
+    pub rows: Vec<Vec<serde_json::Value>>,
+    pub row_count: usize,
+    pub total_count: i64,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LookupDatabaseResult {
+    pub database: String,
+    pub tables: Vec<LookupTableMatch>,
+    pub error: Option<String>,
+    pub search_time_ms: u128,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EntityLookupResult {
+    pub column_name: String,
+    pub value: String,
+    pub databases: Vec<LookupDatabaseResult>,
+    pub total_databases_searched: usize,
+    pub total_tables_matched: usize,
+    pub total_rows_found: usize,
+    pub total_time_ms: u128,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LookupProgress {
+    pub lookup_id: String,
+    pub database: String,
+    pub status: String,
+    pub tables_found: usize,
+    pub rows_found: usize,
+    pub error: Option<String>,
+    pub completed: usize,
+    pub total: usize,
+}

src-tauri/src/models/mod.rs

@@ -1,5 +1,7 @@
+pub mod ai;
 pub mod connection;
 pub mod history;
+pub mod lookup;
 pub mod management;
 pub mod query_result;
 pub mod saved_queries;