fix(file-service): add Flyway migration for pinned column, fix production crash

file-service uses ddl-auto=validate (Flyway-managed schema), not auto-DDL — the
previous commit added a pinned field to FileEntity with no matching migration,
so Hibernate schema validation failed at startup and crash-looped the service
in production. Add V2__add_pinned.sql to actually create the column.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

file-service/src/main/java/com/xuqm/file/entity/FileEntity.java

@@ -46,7 +46,7 @@ public class FileEntity {
      * services (e.g. update-service) for files that must stay downloadable indefinitely,
      * such as APK packages, even if nobody re-downloads them for a long time.
      */
-    @Column(name = "pinned", nullable = false)
+    @Column(name = "pinned", nullable = false, columnDefinition = "TINYINT(1) NOT NULL DEFAULT 0")
     private boolean pinned;
 
     public String getId() { return id; }

file-service/src/main/resources/db/migration/V2__add_pinned.sql

@@ -0,0 +1,2 @@
+ALTER TABLE file_record
+    ADD COLUMN pinned TINYINT(1) NOT NULL DEFAULT 0;