feat(endpoint): 端点默认 body_rules 机制与 Codex 规则回填

- EndpointDefinition 新增 default_body_rules 字段，openai:cli/compact 配置 Codex 默认规则
- 创建端点时若未指定 body_rules 则自动填充对应格式的默认值
- 新增 GET /defaults/{api_format}/body-rules 接口查询默认规则
- 前端 EndpointFormDialog 增加"重置请求体"按钮，支持一键恢复默认
- Alembic 迁移回填已有 Codex 端点的默认 body_rules
- 新增 metadata 和 endpoint 创建默认值的单元测试

alembic/versions/20260302_1500_dd0278c0a28c_backfill_codex_default_body_rules.py

@@ -0,0 +1,69 @@
+"""backfill_codex_default_body_rules
+
+Backfill default body_rules for openai:cli and openai:compact endpoints
+that currently have body_rules IS NULL.
+
+Rules:
+- drop max_output_tokens
+- drop temperature
+- drop top_p
+- set store = false
+- set instructions = "You are GPT-5." (when instructions not exists)
+
+Revision ID: dd0278c0a28c
+Revises: 1d2e3f4a5b6c
+Create Date: 2026-03-02 15:00:00.000000+00:00
+"""
+
+from __future__ import annotations
+
+import json
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "dd0278c0a28c"
+down_revision = "1d2e3f4a5b6c"
+branch_labels = None
+depends_on = None
+
+_TARGET_FORMATS = ("openai:cli", "openai:compact")
+
+_DEFAULT_BODY_RULES = [
+    {"action": "drop", "path": "max_output_tokens"},
+    {"action": "drop", "path": "temperature"},
+    {"action": "drop", "path": "top_p"},
+    {"action": "set", "path": "store", "value": False},
+    {
+        "action": "set",
+        "path": "instructions",
+        "value": "You are GPT-5.",
+        "condition": {"path": "instructions", "op": "not_exists"},
+    },
+]
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # 幂等性: 仅回填 body_rules 为空（SQL NULL 或 JSON null）的记录
+    rules_json = json.dumps(_DEFAULT_BODY_RULES, ensure_ascii=False)
+    result = conn.execute(
+        sa.text("""
+            UPDATE provider_endpoints
+            SET body_rules = CAST(:rules AS json),
+                updated_at = CURRENT_TIMESTAMP
+            WHERE api_format IN (:fmt1, :fmt2)
+              AND (body_rules IS NULL OR body_rules::text = 'null')
+        """),
+        {"rules": rules_json, "fmt1": _TARGET_FORMATS[0], "fmt2": _TARGET_FORMATS[1]},
+    )
+    if result.rowcount:
+        print(f"  backfilled body_rules for {result.rowcount} endpoint(s)")
+
+
+def downgrade() -> None:
+    # Data backfill: no-op to avoid removing user-customized rules.
+    return