feat(ui): spinners for ConPTY session start and task refine

Both actions previously gave no feedback: opening a ConPTY session only created
the tile after the launch-spec roundtrip (which may build a worktree), and the
refine button just disappeared while the run was in flight.

Add a shared Ellipse.spinner style, and let ConPtyPaneViewModel resolve its own
launch spec so the tile shows up immediately with a starting overlay. A failed
launch now keeps the tile with its inline error banner instead of never
appearing — Start() is separated from the ctor so the host can subscribe to
ErrorReported before the launch begins.

src/ClaudeDo.Localization/locales/de.json

@@ -160,7 +160,8 @@
     "feedbackLabel": "FEEDBACK FÜR DEN AGENTEN",
     "feedbackPlaceholder": "Was soll der Agent korrigieren?",
     "rerun": "Erneut ausführen",
-    "refineTip": "Aufgabe mit Claude verfeinern"
+    "refineTip": "Aufgabe mit Claude verfeinern",
+    "refiningTip": "Claude verfeinert diese Aufgabe…"
   },
   "lists": {
     "heading": "Listen",
@@ -267,6 +268,7 @@
     "overviewMode": "Übersicht",
     "closeSession": "Sitzung schließen",
     "conptyLaunchFailed": "ConPTY-Sitzung konnte nicht geöffnet werden: {0}",
+    "conptyStarting": "Sitzung wird gestartet…",
     "mergeHelperTitle": "Merge-Helfer",
     "submitForReviewFailed": "Einreichen zum Review fehlgeschlagen: {0}",
     "submitForReview": "Zum Review einreichen",