feat(fingerprint): 引入 per-key 请求指纹系统，替代全局 TLS 指纹开关

为每个 ProviderAPIKey 生成并持久化独立的请求指纹配置，涵盖 TLS impersonate
profile、浏览器 UA、Stainless SDK 头部、Node/Chrome/Electron 版本等维度。
指纹基于 key ID 确定性生成，支持手动编辑和批量重新生成。

- 新增 fingerprint 模块：生成、加载、校验、懒持久化
- 数据库迁移：provider_api_keys 新增 fingerprint JSON 列
- 请求链路注入：handler 基类设置上下文指纹，request_builder 和 envelope 消费
- HTTP Client 支持动态 impersonate profile 选择
- Antigravity 适配器使用指纹覆盖 UA/session/Node 版本
- 前端移除手动 TLS 指纹开关，新增批量 regenerate_fingerprint 操作
- 号池管理 UI 优化：token 缩写格式、blocked 行样式、时间显示改为日期格式

tests/services/test_provider_fingerprint.py

@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+from src.services.provider.fingerprint import (
+    CHROME_IMPERSONATE_PROFILES,
+    ensure_key_fingerprint,
+    generate_fingerprint,
+    load_fingerprint,
+)
+
+
+def test_generate_fingerprint_is_deterministic_with_seed() -> None:
+    first = generate_fingerprint(seed="key-123")
+    second = generate_fingerprint(seed="key-123")
+    assert first == second
+
+
+def test_load_fingerprint_falls_back_for_invalid_impersonate() -> None:
+    profile = load_fingerprint({"impersonate": "invalid-profile"}, "key-abc")
+    assert profile.impersonate in CHROME_IMPERSONATE_PROFILES
+
+
+def test_ensure_key_fingerprint_returns_profile_when_missing() -> None:
+    key = SimpleNamespace(id="key-xyz", fingerprint=None)
+    profile = ensure_key_fingerprint(key, persist_if_missing=False)
+
+    assert profile.impersonate in CHROME_IMPERSONATE_PROFILES
+    # Deterministic: same key_id produces same profile
+    profile2 = ensure_key_fingerprint(key, persist_if_missing=False)
+    assert profile.impersonate == profile2.impersonate
+
+
+def test_ensure_key_fingerprint_uses_existing_fingerprint() -> None:
+    existing = generate_fingerprint(seed="key-existing")
+    key = SimpleNamespace(id="key-existing", fingerprint=existing)
+    profile = ensure_key_fingerprint(key, persist_if_missing=False)
+
+    assert profile.impersonate == existing["impersonate"]