feat: add HTTP/SOCKS5 proxy support for API endpoints

- Add proxy field to ProviderEndpoint database model with migration
- Add ProxyConfig Pydantic model for proxy URL validation
- Extend HTTP client pool with create_client_with_proxy method
- Integrate proxy configuration in chat_handler_base.py and cli_handler_base.py
- Update admin API endpoints to support proxy configuration CRUD
- Add proxy configuration UI in frontend EndpointFormDialog

Fixes #28

alembic/versions/20251218_0631_f30f9936f6a2_add_proxy_field_to_provider_endpoints.py

@@ -0,0 +1,57 @@
+"""add proxy field to provider_endpoints
+
+Revision ID: f30f9936f6a2
+Revises: 1cc6942cf06f
+Create Date: 2025-12-18 06:31:58.451112+00:00
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy import inspect
+
+# revision identifiers, used by Alembic.
+revision = 'f30f9936f6a2'
+down_revision = '1cc6942cf06f'
+branch_labels = None
+depends_on = None
+
+
+def column_exists(table_name: str, column_name: str) -> bool:
+    """检查列是否存在"""
+    bind = op.get_bind()
+    inspector = inspect(bind)
+    columns = [col['name'] for col in inspector.get_columns(table_name)]
+    return column_name in columns
+
+
+def get_column_type(table_name: str, column_name: str) -> str:
+    """获取列的类型"""
+    bind = op.get_bind()
+    inspector = inspect(bind)
+    for col in inspector.get_columns(table_name):
+        if col['name'] == column_name:
+            return str(col['type']).upper()
+    return ''
+
+
+def upgrade() -> None:
+    """添加 proxy 字段到 provider_endpoints 表"""
+    if not column_exists('provider_endpoints', 'proxy'):
+        # 字段不存在，直接添加 JSONB 类型
+        op.add_column('provider_endpoints', sa.Column('proxy', JSONB(), nullable=True))
+    else:
+        # 字段已存在，检查是否需要转换类型
+        col_type = get_column_type('provider_endpoints', 'proxy')
+        if 'JSONB' not in col_type:
+            # 如果是 JSON 类型，转换为 JSONB
+            op.execute(
+                'ALTER TABLE provider_endpoints '
+                'ALTER COLUMN proxy TYPE JSONB USING proxy::jsonb'
+            )
+
+
+def downgrade() -> None:
+    """移除 proxy 字段"""
+    if column_exists('provider_endpoints', 'proxy'):
+        op.drop_column('provider_endpoints', 'proxy')