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/types/index.ts

@@ -56,12 +56,18 @@ export interface ColumnInfo {
   ordinal_position: number;
   character_maximum_length: number | null;
   is_primary_key: boolean;
+  comment: string | null;
 }
 
 export interface ConstraintInfo {
   name: string;
   constraint_type: string;
   columns: string[];
+  referenced_schema: string | null;
+  referenced_table: string | null;
+  referenced_columns: string[] | null;
+  update_rule: string | null;
+  delete_rule: string | null;
 }
 
 export interface IndexInfo {
@@ -223,8 +229,13 @@ export interface SavedQuery {
   created_at: string;
 }
 
+export type AiProvider = "ollama" | "openai" | "anthropic";
+
 export interface AiSettings {
+  provider: AiProvider;
   ollama_url: string;
+  openai_api_key?: string;
+  anthropic_api_key?: string;
   model: string;
 }
 
@@ -272,7 +283,47 @@ export interface LookupProgress {
   total: number;
 }
 
-export type TabType = "query" | "table" | "structure" | "roles" | "sessions" | "lookup";
+export interface TriggerInfo {
+  name: string;
+  event: string;
+  timing: string;
+  orientation: string;
+  function_name: string;
+  is_enabled: boolean;
+  definition: string;
+}
+
+export interface ErdColumn {
+  name: string;
+  data_type: string;
+  is_nullable: boolean;
+  is_primary_key: boolean;
+}
+
+export interface ErdTable {
+  schema: string;
+  name: string;
+  columns: ErdColumn[];
+}
+
+export interface ErdRelationship {
+  constraint_name: string;
+  source_schema: string;
+  source_table: string;
+  source_columns: string[];
+  target_schema: string;
+  target_table: string;
+  target_columns: string[];
+  update_rule: string;
+  delete_rule: string;
+}
+
+export interface ErdData {
+  tables: ErdTable[];
+  relationships: ErdRelationship[];
+}
+
+export type TabType = "query" | "table" | "structure" | "roles" | "sessions" | "lookup" | "erd";
 
 export interface Tab {
   id: string;