nickserv: add INFO and ALIST

INFO shows an account's registration date and (to its owner) email; ALIST
lists the channels an account founds or has access on. The UTC time
formatter moves to the db module so both services share it.

src/engine/db.rs

@@ -433,6 +433,25 @@ fn now() -> u64 {
     SystemTime::now().duration_since(UNIX_EPOCH).map(|d| d.as_secs()).unwrap_or(0)
 }
 
+// Format a Unix timestamp (seconds) as "YYYY-MM-DD HH:MM:SS UTC", using Howard
+// Hinnant's civil-from-days algorithm so no date crate is needed.
+pub(crate) fn human_time(ts: u64) -> String {
+    let days = (ts / 86400) as i64;
+    let rem = ts % 86400;
+    let (hh, mm, ss) = (rem / 3600, (rem % 3600) / 60, rem % 60);
+    let z = days + 719468;
+    let era = (if z >= 0 { z } else { z - 146096 }) / 146097;
+    let doe = z - era * 146097;
+    let yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let day = doy - (153 * mp + 2) / 5 + 1;
+    let month = if mp < 10 { mp + 3 } else { mp - 9 };
+    let year = y + i64::from(month <= 2);
+    format!("{year:04}-{month:02}-{day:02} {hh:02}:{mm:02}:{ss:02} UTC")
+}
+
 impl Db {
     pub fn open(path: impl Into<PathBuf>, origin: impl Into<String>) -> Self {
         let (log, events) = EventLog::open(path.into(), origin.into());
@@ -643,6 +662,11 @@ impl Db {
         self.channels.get(&key(name))
     }
 
+    /// The account record for `name` (its canonical casing), if registered.
+    pub fn account(&self, name: &str) -> Option<&Account> {
+        self.accounts.get(&key(name))
+    }
+
     /// All registered channels, for listing.
     pub fn channels(&self) -> impl Iterator<Item = &ChannelInfo> {
         self.channels.values()
@@ -929,6 +953,12 @@ mod tests {
         Event::CertAdded { account: account.into(), fp: fp.into() }
     }
 
+    #[test]
+    fn formats_unix_time_as_utc() {
+        assert_eq!(human_time(0), "1970-01-01 00:00:00 UTC");
+        assert_eq!(human_time(1783844590), "2026-07-12 08:23:10 UTC");
+    }
+
     #[test]
     fn glob_matches_hostmasks() {
         assert!(glob_match("*!*@host.example", "bob!~b@host.example"));