✨ Add wall-clock timestamps to last-events buffer

Each event entry in `last-events` is now wrapped as
`{:name <event-type> :t (app.common.time/now)}` so every event carries a
wall-clock timestamp. A new helper `format-last-events` renders the
buffer as a multi-line string with ISO time and delta-since-previous-
event in ms, replacing the previous pprint dump in error reports.

This lets support/devs tell whether the events leading up to a crash
were spaced out (user action) or jammed together (runaway loop).

AI-assisted-by: minimax-m3
Signed-off-by: Andrey Antukh <niwi@niwi.nz>

frontend/src/app/main/errors.cljs

@@ -151,7 +151,7 @@
 
         (println "Last events:")
         (println "--------------------")
-        (pp/pprint @st/last-events {:length 200})
+        (println (st/format-last-events))
         (println)))
     (catch :default cause
       (.error js/console "error on generating report" cause)

frontend/src/app/main/store.cljs

@@ -7,6 +7,7 @@
 (ns app.main.store
   (:require
    [app.common.logging :as log]
+   [app.common.time :as ct]
    [app.util.object :as obj]
    [app.util.timers :as tm]
    [beicon.v2.core :as rx]
@@ -94,6 +95,7 @@
          (rx/filter #(not (contains? omitset %)))
          (rx/map str)
          (rx/pipe (rxo/distinct-contiguous))
+         (rx/map (fn [event] {:name event :t (ct/now)}))
          (rx/scan (fn [buffer event]
                     (cond-> (conj buffer event)
                       (> (count buffer) 50)
@@ -102,6 +104,29 @@
          (rx/subs! #(reset! buffer (vec %))))
     buffer))
 
+(defn format-last-events
+  "Render the `last-events` buffer as a multi-line string with the
+  wall-clock time of each event and the delta (ms) since the previous
+  entry. The first entry has no delta. Useful for embedding in error
+  reports."
+  ([] (format-last-events @last-events))
+  ([events]
+   (let [lines
+         (loop [prev-t nil
+                xs     (seq events)
+                out    (transient [])]
+           (if xs
+             (let [{:keys [name t]} (first xs)
+                   iso  (ct/format-inst t :iso)
+                   tail (if prev-t
+                          (str "  (+" (ct/diff-ms prev-t t) "ms)")
+                          "")]
+               (recur t
+                      (next xs)
+                      (conj! out (str iso tail "  " name))))
+             (persistent! out)))]
+     (str/join "\n" lines))))
+
 (defn emit!
   ([] nil)
   ([event]