fix: 精油编辑统一保存到 DB + 导出 Excel 增加功效列

- 新增 oil_cards 表，持久化知识卡片（功效/用法/方法/注意/emoji）
- POST /api/oils 扩展接受 card_* 字段，在同一事务里 upsert oil_cards
- GET /api/oil-cards 返回全部卡片
- 前端 getOilCard 优先查 DB，再 fallback 静态表
- saveEditOil 统一走 saveOil，不再分两套保存
- 精油价目 Excel 导出增加「功效」列
- 首次部署自动从静态 OIL_CARDS 播种到 oil_cards 表

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/database.py

@@ -123,6 +123,15 @@ def init_db():
             tag_name TEXT NOT NULL,
             sort_order INTEGER DEFAULT 0
         );
+        CREATE TABLE IF NOT EXISTS oil_cards (
+            name TEXT PRIMARY KEY REFERENCES oils(name) ON DELETE CASCADE,
+            emoji TEXT DEFAULT '',
+            en TEXT DEFAULT '',
+            effects TEXT DEFAULT '',
+            usage TEXT DEFAULT '',
+            method TEXT DEFAULT '',
+            caution TEXT DEFAULT ''
+        );
     """)
 
     # Migration: add password and brand fields to users if missing
@@ -341,7 +350,7 @@ def log_audit(conn, user_id, action, target_type=None, target_id=None, target_na
     )
 
 
-def seed_defaults(default_oils_meta: dict, default_recipes: list):
+def seed_defaults(default_oils_meta: dict, default_recipes: list, default_oil_cards: dict = None):
     """Seed DB with defaults if empty."""
     conn = get_db()
     c = conn.cursor()
@@ -379,5 +388,18 @@ def seed_defaults(default_oils_meta: dict, default_recipes: list):
                     (rid, tag),
                 )
 
+    # Seed oil_cards from static data if table is empty
+    if default_oil_cards:
+        card_count = c.execute("SELECT COUNT(*) FROM oil_cards").fetchone()[0]
+        if card_count == 0:
+            for name, card in default_oil_cards.items():
+                c.execute(
+                    "INSERT OR IGNORE INTO oil_cards (name, emoji, en, effects, usage, method, caution) "
+                    "VALUES (?, ?, ?, ?, ?, ?, ?)",
+                    (name, card.get("emoji", ""), card.get("en", ""),
+                     card.get("effects", ""), card.get("usage", ""),
+                     card.get("method", ""), card.get("caution", "")),
+                )
+
     conn.commit()
     conn.close()