fix: secret handling and relation naming logic

Implemented improved handling for secrets in `DbModuleManager`, allowing secret merging and building before saving. Enhanced `ManyToManyRelation` naming to produce valid identifiers and ensured better testing coverage for both changes.

app/__test__/modules/DbModuleManager.spec.ts

@@ -1,6 +1,7 @@
 import { it, expect, describe } from "bun:test";
 import { DbModuleManager } from "modules/db/DbModuleManager";
 import { getDummyConnection } from "../helper";
+import { TABLE_NAME } from "modules/db/migrations";
 
 describe("DbModuleManager", () => {
    it("should extract secrets", async () => {
@@ -19,4 +20,57 @@ describe("DbModuleManager", () => {
       expect(m.toJSON(true).auth.jwt.secret).toBe("test");
       await m.save();
    });
+
+   it("should work with initial secrets", async () => {
+      const { dummyConnection } = getDummyConnection(false);
+      const db = dummyConnection.kysely;
+      const m = new DbModuleManager(dummyConnection, {
+         initial: {
+            auth: {
+               enabled: true,
+               jwt: {
+                  secret: "",
+               },
+            },
+         },
+         secrets: {
+            "auth.jwt.secret": "test",
+         },
+      });
+      await m.build();
+      expect(m.toJSON(true).auth.jwt.secret).toBe("test");
+
+      const getSecrets = () =>
+         db
+            .selectFrom(TABLE_NAME)
+            .selectAll()
+            .where("type", "=", "secrets")
+            .executeTakeFirst()
+            .then((r) => r?.json);
+
+      expect(await getSecrets()).toEqual({ "auth.jwt.secret": "test" });
+
+      // also after rebuild
+      await m.build();
+      await m.save();
+      expect(await getSecrets()).toEqual({ "auth.jwt.secret": "test" });
+
+      // and ignore if already present
+      const m2 = new DbModuleManager(dummyConnection, {
+         initial: {
+            auth: {
+               enabled: true,
+               jwt: {
+                  secret: "",
+               },
+            },
+         },
+         secrets: {
+            "auth.jwt.secret": "something completely different",
+         },
+      });
+      await m2.build();
+      await m2.save();
+      expect(await getSecrets()).toEqual({ "auth.jwt.secret": "test" });
+   });
 });