🐛 fix(duckdb): 修复唯一索引识别与多库对象解析

- 合并 DuckDB 约束与索引元数据，恢复唯一索引表的可编辑判定
- 修复 attach 多库场景下 catalog/schema/table 定位混乱问题
- 统一前后端 qualified name 解析，支持带点和带引号对象名
- 补充 DuckDB 元数据与编辑链路回归测试

frontend/src/utils/qualifiedName.ts

@@ -0,0 +1,126 @@
+export type QualifiedNameParts = {
+  parentPath: string;
+  objectName: string;
+};
+
+const normalizeIdentifierEscapes = (raw: string): string => {
+  let value = String(raw || '').trim();
+  for (let i = 0; i < 4; i += 1) {
+    const next = String(value || '').trim()
+      .replace(/\\\\"/g, '\\"')
+      .replace(/\\"/g, '"');
+    if (next === value) break;
+    value = next;
+  }
+  return String(value || '').trim();
+};
+
+export const stripIdentifierQuotes = (part: string): string => {
+  const text = normalizeIdentifierEscapes(part);
+  if (!text) return '';
+  if (text.length >= 2) {
+    const first = text[0];
+    const last = text[text.length - 1];
+    if (first === '"' && last === '"') {
+      return text.slice(1, -1).replace(/""/g, '"').trim();
+    }
+    if (first === '`' && last === '`') {
+      return text.slice(1, -1).replace(/``/g, '`').trim();
+    }
+    if (first === '[' && last === ']') {
+      return text.slice(1, -1).replace(/]]/g, ']').trim();
+    }
+  }
+  return text;
+};
+
+export const splitQualifiedNameSegments = (qualifiedName: string): string[] => {
+  const text = normalizeIdentifierEscapes(qualifiedName);
+  if (!text) return [];
+
+  const segments: string[] = [];
+  let current = '';
+  let inDouble = false;
+  let inBacktick = false;
+  let inBracket = false;
+
+  const flush = () => {
+    const value = current.trim();
+    current = '';
+    if (!value) return;
+    segments.push(stripIdentifierQuotes(value));
+  };
+
+  for (let i = 0; i < text.length; i += 1) {
+    const ch = text[i];
+
+    if (inDouble) {
+      current += ch;
+      if (ch === '"' && text[i + 1] === '"') {
+        current += text[i + 1];
+        i += 1;
+        continue;
+      }
+      if (ch === '"') inDouble = false;
+      continue;
+    }
+
+    if (inBacktick) {
+      current += ch;
+      if (ch === '`' && text[i + 1] === '`') {
+        current += text[i + 1];
+        i += 1;
+        continue;
+      }
+      if (ch === '`') inBacktick = false;
+      continue;
+    }
+
+    if (inBracket) {
+      current += ch;
+      if (ch === ']' && text[i + 1] === ']') {
+        current += text[i + 1];
+        i += 1;
+        continue;
+      }
+      if (ch === ']') inBracket = false;
+      continue;
+    }
+
+    if (ch === '"') {
+      inDouble = true;
+      current += ch;
+      continue;
+    }
+    if (ch === '`') {
+      inBacktick = true;
+      current += ch;
+      continue;
+    }
+    if (ch === '[') {
+      inBracket = true;
+      current += ch;
+      continue;
+    }
+    if (ch === '.') {
+      flush();
+      continue;
+    }
+    current += ch;
+  }
+
+  flush();
+  return segments;
+};
+
+export const splitQualifiedName = (qualifiedName: string): QualifiedNameParts => {
+  const segments = splitQualifiedNameSegments(qualifiedName);
+  if (segments.length === 0) return { parentPath: '', objectName: '' };
+  if (segments.length === 1) return { parentPath: '', objectName: segments[0] };
+  return {
+    parentPath: segments.slice(0, -1).join('.'),
+    objectName: segments[segments.length - 1],
+  };
+};
+
+export const splitQualifiedNameLast = splitQualifiedName;