Rework sidebar pages

* Move sidebar pages from workspace to space level
* Replace array sorting with lexicographical fractional indexing
* Fixes and updates

apps/server/src/kysely/migrations/20240413T164028-add-position-to-pages.ts

@@ -0,0 +1,12 @@
+import { type Kysely } from 'kysely';
+
+export async function up(db: Kysely<any>): Promise<void> {
+  await db.schema
+    .alterTable('pages')
+    .addColumn('position', 'varchar', (col) => col)
+    .execute();
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await db.schema.alterTable('pages').dropColumn('position').execute();
+}