feat: add column sort, SQL formatter, table stats, insert dialog, saved queries & sessions monitor

- Column sort by header click in table view (ASC/DESC/none cycle, server-side)
- SQL formatter with Format button and Shift+Alt+F keybinding (sql-formatter)
- Table size and row count display in schema tree via pg_class
- Insert row dialog with column type hints and auto-skip for identity columns
- Saved queries (bookmarks) with CRUD backend, sidebar panel, and save dialog
- Active sessions monitor (pg_stat_activity) with auto-refresh, cancel & terminate

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

src-tauri/src/models/management.rs

@@ -79,6 +79,19 @@ pub struct TablePrivilege {
     pub is_grantable: bool,
 }
 
+#[derive(Debug, Serialize, Deserialize)]
+pub struct SessionInfo {
+    pub pid: i32,
+    pub usename: Option<String>,
+    pub datname: Option<String>,
+    pub state: Option<String>,
+    pub query: Option<String>,
+    pub query_start: Option<String>,
+    pub wait_event_type: Option<String>,
+    pub wait_event: Option<String>,
+    pub client_addr: Option<String>,
+}
+
 #[derive(Debug, Deserialize)]
 pub struct GrantRevokeParams {
     pub action: String,