Show the mod pack an instance uses in the web UI (#1177)

InstanceDetails now carries factorio.mod_pack_id as modPackId, so the
instance list and pages can show it without fetching each config. The
web UI resolves an unset value to the controller default and tags it
"Default". The name links to the mod pack page.

Closes #852

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/controller/InstanceRecord.test.js

@@ -153,6 +153,17 @@ describe("controller/InstanceRecord", function () {
 			assert.equal(details.startedAtMs, 100);
 			assert.equal(details.updatedAtMs, 200);
 			assert.equal(details.excludeFromStartAll, false);
+			assert.equal(details.modPackId, undefined);
+		});
+
+		it("should include the mod pack set in the config", function () {
+			const config = new lib.InstanceConfig("controller", {
+				"instance.id": 1,
+				"instance.name": "TestInstance",
+				"factorio.mod_pack_id": 3,
+			});
+			const details = new InstanceRecord(config, "stopped").toInstanceDetails();
+			assert.equal(details.modPackId, 3);
 		});
 	});