Hot-reload content on a NATS trigger instead of requiring a restart

questions is now Arc<ArcSwap<HashMap<...>>> - readers do a lock-free
atomic load (state.questions.load().get(&id).cloned()), never blocking
on or blocked by a reload. content::watch_for_reload subscribes to
portal.content.reload (published by the questions repo's own CI after
it lints a push - see that repo's lint-and-reload.yml) and swaps in a
freshly re-fetched HashMap on each message. A fetch/parse failure logs
and keeps serving the last-good content rather than clearing it.

Cargo.toml

@@ -22,6 +22,7 @@ tower = { version = "0.5", optional = true }
 tower-http = { version = "0.6", features = ["fs"], optional = true }
 tower-sessions = { version = "0.14", optional = true }
 async-nats = { version = "0.38", optional = true }
+arc-swap = { version = "1", optional = true }
 url = { version = "2", optional = true }
 serde_yaml = { version = "0.9", optional = true }
 sha2 = { version = "0.10", optional = true }
@@ -76,6 +77,7 @@ ssr = [
     "dep:tower-http",
     "dep:tower-sessions",
     "dep:async-nats",
+    "dep:arc-swap",
     "dep:url",
     "dep:serde_yaml",
     "dep:sha2",