docs: fix RETAIN syntax ambiguity and add anchor to snapshot tag links

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: zhyass

docs/cn/sql-reference/10-sql-commands/00-ddl/21-table-versioning/01-create-snapshot-tag.md

@@ -29,7 +29,7 @@ ALTER TABLE [<database_name>.]<table_name> CREATE TAG <tag_name>
         OFFSET => <time_interval> |
         TAG => <tag_name>
     ) ]
-    [ RETAIN <n> DAYS | SECONDS ]
+    [ RETAIN <n> { DAYS | SECONDS } ]
 ```
 
 ## 参数

docs/cn/sql-reference/10-sql-commands/00-ddl/21-table-versioning/index.md

@@ -31,7 +31,7 @@ SET enable_experimental_table_ref = 1;
 快照标签为快照附加一个可读的名称。只要标签存在，被引用的快照就会受到保护，不会被 vacuum 和垃圾回收清理 — 即使保留期已过。
 
 - 不带 `RETAIN` 的标签会一直存在，直到显式删除。
-- 带 `RETAIN <n> DAYS | SECONDS` 的标签会在指定时间后，在下次 vacuum 操作时自动移除。
+- 带 `RETAIN <n> { DAYS | SECONDS }` 的标签会在指定时间后，在下次 vacuum 操作时自动移除。
 
 **SQL 命令：**
 

docs/en/sql-reference/10-sql-commands/00-ddl/21-table-versioning/01-create-snapshot-tag.md

@@ -29,7 +29,7 @@ ALTER TABLE [<database_name>.]<table_name> CREATE TAG <tag_name>
         OFFSET => <time_interval> |
         TAG => <tag_name>
     ) ]
-    [ RETAIN <n> DAYS | SECONDS ]
+    [ RETAIN <n> { DAYS | SECONDS } ]
 ```
 
 ## Parameters

docs/en/sql-reference/10-sql-commands/00-ddl/21-table-versioning/index.md

@@ -31,7 +31,7 @@ Snapshot tags pin a specific point-in-time state of a table by name. Once create
 A snapshot tag attaches a human-readable name to a snapshot. As long as the tag exists, the referenced snapshot is protected from vacuum and garbage collection — even if the retention period has passed.
 
 - A tag without `RETAIN` lives until explicitly dropped.
-- A tag with `RETAIN <n> DAYS | SECONDS` is automatically removed after the specified duration during the next vacuum operation.
+- A tag with `RETAIN <n> { DAYS | SECONDS }` is automatically removed after the specified duration during the next vacuum operation.
 
 **SQL Commands:**