feat: PWA restores last project + playhead/stack on reopen

A homescreen launch opens the manifest start_url ("/") with no route, so the
deep state was lost. Persist the in-app URL (already kept current with stack +
playhead) to localStorage, and on a standalone cold launch with a bare hash,
re-enter it before the router reads the URL. Browser tabs are unaffected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tl/src/tl/core.cljs

@@ -29,6 +29,7 @@
 (defn init []
   (re-frame/dispatch-sync [::events/initialize-db])
   (re-frame/dispatch [::events/fetch-me])
+  (routes/restore-last!)        ; PWA: re-enter the last URL before the router reads it
   (routes/start! route!)
   (dev-setup)
   (mount-root))

tl/src/tl/routes.cljs

@@ -66,10 +66,28 @@
     (str (href :project/show {:id id}) query)))
 
 (defonce ^:private last-replaced (atom nil))
+(def ^:private last-url-key "tl/last-url")
 
 (defn replace-project-state! [{:keys [id stack playhead]}]
   (when id
     (let [url (project-url id stack playhead)]
       (when (not= url @last-replaced)
         (reset! last-replaced url)
-        (.replaceState js/history nil "" url)))))
+        (.replaceState js/history nil "" url)
+        ;; remember where we were so an installed PWA can come back here
+        (.setItem js/localStorage last-url-key url)))))
+
+(defn- standalone?
+  "Running as an installed PWA (added to homescreen), not a browser tab."
+  []
+  (or (some-> (.matchMedia js/window "(display-mode: standalone)") .-matches)
+      (true? (.-standalone js/navigator))))
+
+(defn restore-last!
+  "A cold PWA launch opens the manifest start_url ('/') with no route, dropping
+   the last project + playhead/stack. If we booted bare in standalone mode and
+   have a saved location, put it in the hash before the router reads it."
+  []
+  (when (and (standalone?) (contains? #{"" "#"} (.. js/window -location -hash)))
+    (when-let [saved (.getItem js/localStorage last-url-key)]
+      (set! (.. js/window -location -hash) saved))))