fix(kb): replace fragile error string matching with pre-check for duplicate kb_name

[lxfight]

创建知识库时，原有的重复名称检测依赖于捕获所有异常后检查 "kb_name" in str(e)，这种字符串匹配方式脆弱且不可靠。

Modifications / 改动点

• astrbot/core/knowledge_base/kb_mgr.py: 在创建知识库前预先查询名称是否已存在，如果存在直接抛出明确的 ValueError 异常。避免依赖异常字符串匹配合法性检查

• This is NOT a breaking change. / 这不是一个破坏性变更。

Screenshots or Test Results / 运行截图或测试结果

tests/ -k "kb" 19 passed

---

Checklist / 检查清单

• 😊 If there are new features added in the PR, I have discussed it with the authors through issues/emails, etc.
  / 如果 PR 中有新加入的功能，已经通过 Issue / 邮件等方式和作者讨论过。

• 👀 My changes have been well-tested, and "Verification Steps" and "Screenshots" have been provided above.
  / 我的更改经过了良好的测试，并已在上方提供了"验证步骤"和"运行截图"。

• 🤓 I have ensured that no new dependencies are introduced, OR if new dependencies are introduced, they have been added to the appropriate locations in requirements.txt and pyproject.toml.
  / 我确保没有引入新依赖库，或者引入了新依赖库的同时将其添加到 requirements.txt 和 pyproject.toml 文件相应位置。

• 😮 My changes do not introduce malicious code.
  / 我的更改没有引入恶意代码。

Summary by Sourcery

Improve robustness of knowledge base creation error handling by explicitly checking for duplicate names before creation and logging unexpected failures.

Bug Fixes:

• Prevent fragile duplicate knowledge base name detection that relied on matching substrings in exception messages.

Enhancements:

• Add a pre-query for existing knowledge base names and raise a clear ValueError when a duplicate is found.
• Log knowledge base creation failures instead of reinterpreting all exceptions as duplicate name errors.

[gemini-code-assist]

Code Review

This pull request improves the knowledge base creation logic in kb_mgr.py by proactively checking if a knowledge base name already exists before attempting creation, replacing a fragile exception string-matching check. It also adds error logging when creation fails. There are no review comments, so I have no feedback to provide.

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[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• The pre-check for existing kb_name reduces reliance on error string parsing but still leaves a race window; consider also handling the specific database unique constraint violation on insert to cover concurrent creation attempts robustly.
• In the broad except Exception block, logger.exception may be preferable to logger.error so that the full traceback is captured in logs while re-raising the original exception.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The pre-check for existing `kb_name` reduces reliance on error string parsing but still leaves a race window; consider also handling the specific database unique constraint violation on insert to cover concurrent creation attempts robustly.
- In the broad `except Exception` block, `logger.exception` may be preferable to `logger.error` so that the full traceback is captured in logs while re-raising the original exception.

## Individual Comments

### Comment 1
<location path="astrbot/core/knowledge_base/kb_mgr.py" line_range="134" />
<code_context>
                 self.kb_insts[kb.kb_id] = kb_helper
                 return kb_helper
         except Exception as e:
-            if "kb_name" in str(e):
-                raise ValueError(f"知识库名称 '{kb_name}' 已存在")
+            logger.error(f"创建知识库失败: {e}")
             raise
</code_context>
<issue_to_address>
**suggestion (bug_risk):** Reintroduce targeted handling for unique-name violations rather than fully generic error propagation

This change removes the specific mapping of name-uniqueness violations to a clear `ValueError`, so callers will now see a generic exception when a DB uniqueness constraint is hit. To avoid regressing the public behavior, please still detect this known case (ideally via driver-specific error types/codes rather than string matching) and translate it into the same `ValueError` used in the pre-check, so both the pre-check and DB constraint paths remain consistent and user-friendly.

```suggestion
        except Exception as e:
            logger.error(f"创建知识库失败: {e}")

            # 尝试识别数据库层面的唯一约束冲突（例如名称重复）
            unique_violation = False

            # 优先使用 SQLAlchemy 的 IntegrityError 等驱动特定异常
            try:
                from sqlalchemy.exc import IntegrityError  # type: ignore
            except Exception:  # pragma: no cover - 兼容未使用 SQLAlchemy 的情况
                IntegrityError = ()  # type: ignore

            if isinstance(e, IntegrityError):
                # PostgreSQL: 通过 pgcode 判断唯一约束冲突
                orig = getattr(e, "orig", None)
                pgcode = getattr(orig, "pgcode", None)
                if pgcode == "23505":
                    unique_violation = True

                # 兜底：通过错误信息中是否包含 unique/constraint 等关键词判断
                msg = str(e).lower()
                if "unique constraint" in msg or "unique violation" in msg:
                    unique_violation = True
            else:
                # 非特定驱动时，保留原有的基于错误信息的判断逻辑
                if "kb_name" in str(e):
                    unique_violation = True

            if unique_violation:
                # 保持与前置名称检查相同的对外行为
                raise ValueError(f"知识库名称 '{kb_name}' 已存在") from e

            # 非唯一约束错误继续向外抛出
            raise
```
</issue_to_address>

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