chore: 연습문제 '시작하기 전에' 섹션 제거 (30개 파일)

사용 테이블 + 학습 범위 admonition으로 역할 대체.
트랜잭션 경고(warning)는 유지.

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

Author: civilian7

docs/en/exercises/advanced-01-window-functions.md

@@ -12,12 +12,6 @@
 !!! abstract "Concepts"
     `ROW_NUMBER`, `RANK`, `DENSE_RANK`, `NTILE`, `LAG`, `LEAD`, `SUM/AVG/COUNT OVER`, `FIRST_VALUE`, `LAST_VALUE`, `ROWS BETWEEN`
 
-!!! info "Before You Begin"
-    This exercise puts into practice what you learned in **Advanced Lesson 18** (Window Functions).
-    All queries can be executed in SQLite. Cancellation/return order exclusion conditions: `status NOT IN ('cancelled', 'returned', 'return_requested')`
-
----
-
 ## Basic (1~5)
 
 Practice the basic syntax of window functions.

docs/en/exercises/advanced-02-cte.md

@@ -12,13 +12,6 @@
 !!! abstract "Concepts"
     `WITH`, Recursive CTE(`WITH RECURSIVE`), Multiple CTE Chaining, CTE + Aggregate/JOIN/Window Function
 
-!!! info "Before You Begin"
-    This exercise puts into practice what you learned in **Advanced Lesson 19** (CTE).
-    Recursive CTEs are used in SQLite with the `WITH RECURSIVE` syntax.
-    Cancellation/return order exclusion conditions: `status NOT IN ('cancelled', 'returned', 'return_requested')`
-
----
-
 ## Basic (1~5)
 
 Practice single CTE and CTE + JOIN/aggregation.

docs/en/exercises/advanced-03-exists-antipattern.md

@@ -14,13 +14,6 @@
 !!! abstract "Concepts"
     `EXISTS`, `NOT EXISTS`, Correlated subquery, Anti-join pattern, Universal Quantification
 
-!!! info "Before You Begin"
-    This exercise puts into practice what you learned in **Advanced Lesson 20** (EXISTS).
-    `EXISTS` returns TRUE if there is at least one row as a result of the subquery.
-    `NOT EXISTS` is the opposite — TRUE when there are no rows of results.
-
----
-
 ## Basic (1~5)
 
 Practice the basic usage of EXISTS and NOT EXISTS.

docs/en/exercises/advanced-04-db-objects.md

@@ -14,13 +14,6 @@
 !!! abstract "Concepts"
     `CREATE VIEW`, View query, `DROP VIEW`, `CREATE TRIGGER` (AFTER/BEFORE, INSERT/UPDATE/DELETE, WHEN, OLD/NEW), Audit Logging, Stored procedure concepts (MySQL/PG)
 
-!!! info "Before You Begin"
-    This exercise puts into practice what you learned in **Advanced Lesson 22** (Views), **Lecture 24** (Trigger), and **Lecture 26** (Stored Procedures).
-    Views and triggers can be run in SQLite.
-    Stored procedure questions (15-20) are provided under the MySQL/PostgreSQL tab.
-
----
-
 ## Views (1~7)
 
 Practice creating, using, and managing views.

docs/en/exercises/beginner-02-sort-paging.md

@@ -10,12 +10,6 @@
 !!! abstract "Concepts"
     `SELECT`, `WHERE`, `ORDER BY`, `LIMIT`, `OFFSET`, `DISTINCT`, Aliases (`AS`), arithmetic operations
 
-!!! info "Before You Begin"
-    This exercise uses only what you learned in **Introductory Lessons 1-3** (SELECT, WHERE, ORDER BY, LIMIT, OFFSET).
-    JOINs, subqueries, GROUP BY, and aggregate functions are not used.
-
----
-
 ## Basic (1~10)
 
 Practice one concept at a time.

docs/en/exercises/beginner-03-aggregates.md

@@ -10,13 +10,6 @@
 !!! abstract "Concepts"
     `COUNT`, `SUM`, `AVG`, `MIN`, `MAX`, `ROUND`, `COUNT(DISTINCT)` + Previous lecture contents
 
-!!! info "Before You Begin"
-    This exercise uses only what you learned in **Introduction Lessons 1-4**.
-    GROUP BY, HAVING, JOIN, and subqueries are not used.
-    Aggregate functions return one result for **entire rows** filtered by WHERE.
-
----
-
 ## Basic (1~10)
 
 Practice one aggregate function at a time.