Updates: when a release may install by itself, as a state machine

Issue #52: once a newer release is known, wait for a quiet moment, ask
for 30 seconds, and install unless the answer is no. The caller says
what busy and idle are. Host-tested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

lib/release/src/update_check.h

@@ -24,6 +24,12 @@ inline bool shouldAnnounce(const Release& latest, const std::string& running, co
     return isNewer(latest, running) && latest.tag != failed && latest.tag != announced;
 }
 
+// Should the background check offer to install it by itself (issue #52)? Any newer release, each
+// day it is still the newest; never a version that rolled back on this device.
+inline bool shouldInstall(const Release& latest, const std::string& running, const std::string& failed) {
+    return isNewer(latest, running) && latest.tag != failed;
+}
+
 // Is `url` a download this device takes from the project's server, for this repository? Whatever
 // the API says, the device only fetches from where it asked (a redirected or rewritten answer
 // can't send it elsewhere).