feat: add connection management UI

Add TypeScript types, typed Tauri invoke wrappers, Zustand store,
TanStack Query hooks, and connection components: ConnectionDialog
(create/edit/test), ConnectionList (sheet panel), ConnectionSelector
(toolbar dropdown).

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

src/types/index.ts

@@ -0,0 +1,66 @@
+export interface ConnectionConfig {
+  id: string;
+  name: string;
+  host: string;
+  port: number;
+  user: string;
+  password: string;
+  database: string;
+  ssl_mode?: string;
+  color?: string;
+}
+
+export interface QueryResult {
+  columns: string[];
+  types: string[];
+  rows: unknown[][];
+  row_count: number;
+  execution_time_ms: number;
+}
+
+export interface PaginatedQueryResult extends QueryResult {
+  total_rows: number;
+  page: number;
+  page_size: number;
+}
+
+export interface SchemaObject {
+  name: string;
+  object_type: string;
+  schema: string;
+}
+
+export interface ColumnInfo {
+  name: string;
+  data_type: string;
+  is_nullable: boolean;
+  column_default: string | null;
+  ordinal_position: number;
+  character_maximum_length: number | null;
+  is_primary_key: boolean;
+}
+
+export interface ConstraintInfo {
+  name: string;
+  constraint_type: string;
+  columns: string[];
+}
+
+export interface IndexInfo {
+  name: string;
+  definition: string;
+  is_unique: boolean;
+  is_primary: boolean;
+}
+
+export type TabType = "query" | "table" | "structure";
+
+export interface Tab {
+  id: string;
+  type: TabType;
+  title: string;
+  connectionId: string;
+  schema?: string;
+  table?: string;
+  sql?: string;
+}