feat: add ER diagram and enhance TableStructure with FK details, triggers, comments

- Add interactive ER diagram with ReactFlow + dagre auto-layout, accessible
  via right-click context menu on schema nodes in the sidebar
- Enhance TableStructure: column comments, FK referenced table/columns,
  ON UPDATE/DELETE rules, new Triggers tab
- Backend: rewrite get_table_constraints using pg_constraint for proper
  composite FK support, add get_table_triggers and get_schema_erd commands

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/lib/tauri.ts

@@ -11,6 +11,8 @@ import type {
   ColumnInfo,
   ConstraintInfo,
   IndexInfo,
+  TriggerInfo,
+  ErdData,
   HistoryEntry,
   SavedQuery,
   SessionInfo,
@@ -115,6 +117,15 @@ export const getTableIndexes = (
   table: string
 ) => invoke<IndexInfo[]>("get_table_indexes", { connectionId, schema, table });
 
+export const getTableTriggers = (
+  connectionId: string,
+  schema: string,
+  table: string
+) => invoke<TriggerInfo[]>("get_table_triggers", { connectionId, schema, table });
+
+export const getSchemaErd = (connectionId: string, schema: string) =>
+  invoke<ErdData>("get_schema_erd", { connectionId, schema });
+
 // Data
 export const getTableData = (params: {
   connectionId: string;