fix: Add unique index on tags(blog_id, name) to prevent duplicate tags

Duplicate tags accumulated when the edit flow's deleteBlogTags() silently
failed (due to val() precision loss on BIGINT IDs) while saveTags() still
inserted new rows. Cleaned up 97 existing duplicates and added a database
constraint to prevent recurrence.

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

Author: bpamiri

app/migrator/migrations/20260217180000_add_unique_index_tags_blog_id_name.cfc

@@ -0,0 +1,36 @@
+component extends="wheels.migrator.Migration" hint="adds unique index on tags(blog_id, name) to prevent duplicate tags per blog post" {
+
+	function up() {
+		transaction {
+			try {
+				execute("CREATE UNIQUE INDEX idx_tags_blog_id_name ON tags (blog_id, name)");
+			} catch (any ex) {
+				local.exception = ex;
+			}
+
+			if (StructKeyExists(local, "exception")) {
+				transaction action="rollback";
+				Throw(errorCode = "1", detail = local.exception.detail, message = local.exception.message, type = "any");
+			} else {
+				transaction action="commit";
+			}
+		}
+	}
+
+	function down() {
+		transaction {
+			try {
+				execute("DROP INDEX IF EXISTS idx_tags_blog_id_name");
+			} catch (any ex) {
+				local.exception = ex;
+			}
+
+			if (StructKeyExists(local, "exception")) {
+				transaction action="rollback";
+				Throw(errorCode = "1", detail = local.exception.detail, message = local.exception.message, type = "any");
+			} else {
+				transaction action="commit";
+			}
+		}
+	}
+}