App 2.16.0, server 2.6.0: over-the-air updates from our own repository

The car updates itself again, from this fork's own releases, while the
repository stays private:

- publish-car (flake) creates the pre-release car-<version> on the
  forge and attaches the APK and its .sha256. It needs a forge token
  that may write releases, from ~/.config/nilsmg4/forge-token or
  $FORGE_TOKEN; it is sent in a header and never printed.
- The server relays releases and attachments (/v1/app/releases,
  /v1/app/assets/...), read with a read-only FORGE_TOKEN from its
  Secret, GitHub-shaped with download URLs back at itself. Redirects
  away from the forge are not followed; off (404) without a token.
- The app asks its server with its own paired token, allows exactly
  the server's host, downloads the APK itself instead of through the
  DownloadManager (so the token stays in the app), verifies SHA-256 and
  package name, and tries a PackageInstaller session (it may install
  silently as the system user) before falling back to Downloads.

OTA.md is rewritten for this flow; the k8s and server READMEs explain
the new token.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QLJfZQZeAKAwSqViTmLzki

server/api.go

@@ -19,6 +19,7 @@ import (
 //	GET  /v1/consumption/history/{installationId} the car reads its own totals back
 //	GET  /v1/health                              unauthenticated liveness probe
 //	     /v1/settings/…, /settings                settings typed on a phone (handoff_http.go)
+//	GET  /v1/app/…                               app updates from the forge (releases.go)
 //
 // A car authenticates with the shared INGEST_TOKEN or with its own token from pairing
 // (pairing_http.go).
@@ -28,6 +29,8 @@ type API struct {
 	Pairing     *Pairing
 	// Handoff carries settings typed on a phone to the car (handoff.go).
 	Handoff *Handoff
+	// Releases relays the app's releases from the private forge to the car (releases.go).
+	Releases *Releases
 	// PublicURL is the server's address as a phone reaches it, for the pairing QR code;
 	// derived from the request when empty.
 	PublicURL string
@@ -46,6 +49,7 @@ func (a *API) Routes() http.Handler {
 	mux.HandleFunc("GET /v1/consumption/history/{installationId}", a.ingest(a.history))
 	a.pairingRoutes(mux)
 	a.handoffRoutes(mux)
+	a.releaseRoutes(mux)
 	return mux
 }