Apply DB limit to the maximum note text length (#5465)

src/misc/hard-limits.ts

@@ -0,0 +1,8 @@
+
+// If you change DB_* values, you must also change the DB schema.
+
+/**
+ * Maximum note text length that can be stored in DB.
+ * Surrogate pairs count as one
+ */
+export const DB_MAX_NOTE_TEXT_LENGTH = 8192;