Add release channels as instance version targets

An instance's factorio.version can now target a release channel such as
"stable" or "experimental" (any key from factorio.com/api/latest-releases)
in addition to "latest" and specific X.Y / X.Y.Z versions.

The controller proxies the latest-releases API through a ValueCache and
persists the last successful response to latest-releases.json, serving that
copy when the API is unreachable. On instance start the host resolves a
channel to the concrete version it points to and feeds it into the existing
checkForUpdates/findVersion path, so a channel auto-installs and runs like a
pinned version. The version selector in the web UI lists the available
channels alongside "latest".

Also clarifies the host log/error when a newer version cannot be downloaded
automatically because the host uses a direct (single-version) Factorio
install rather than a versioned directory.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/controller/src/BaseConnection.ts

@@ -33,6 +33,7 @@ export default class BaseConnection extends lib.Link {
 		this.handle(lib.ModPackGetDefaultRequest, this.handleModPackGetDefaultRequest.bind(this));
 		this.handle(lib.ModDownloadRequest, this.handleModDownloadRequest.bind(this));
 		this.handle(lib.FactorioVersionsRequest, this.handleFactorioVersionsRequest.bind(this));
+		this.handle(lib.LatestReleasesRequest, this.handleLatestReleasesRequest.bind(this));
 
 		this.handle(lib.SubscriptionRequest, this.handleSubscriptionRequest.bind(this));
 		this.connector.on("close", () => {
@@ -113,4 +114,8 @@ export default class BaseConnection extends lib.Link {
 	async handleFactorioVersionsRequest(request: lib.FactorioVersionsRequest) {
 		return await this._controller.factorioVersions.get(request.maxAgeMs);
 	}
+
+	async handleLatestReleasesRequest(request: lib.LatestReleasesRequest) {
+		return await this._controller.latestReleases.get(request.maxAgeMs);
+	}
 }