feat(ui): Task-Zeile entdichten und Kontextmenü gruppieren (UX-Struktur A)

Gruppe 1 (Send to queue, Remove from queue, Cancel execution, Open quick
session, Refine task) ist jetzt fix sichtbar und gated per IsEnabled + Grund
statt komplett auszublenden. Planning/Schedule wandern in Untermenüs (Mark as
existierte bereits); der Planning-Kopf zeigt einen Grund, wenn er sonst leer
wäre. Refine-Button, ungesetzter Star und Dequeue-X erscheinen nur bei
Hover-oder-Selektion (TaskRowViewModel.ShowRowActions); ein gesetzter Star und
der Refining-Spinner bleiben immer sichtbar. Der Branch-Chip wandert aus der
Zeile in eine Meta-Zeile in TaskHeaderBar.

A3 headless verifiziert: Avalonia 12 zeigt ToolTips auf IsEnabled=false
Controls nur mit ToolTip.ShowOnDisabled="True" (Default ist false) — dieses
Attached Property existiert bereits und wird für die neuen Disabled-Reason-
Tooltips genutzt.

src/ClaudeDo.Localization/locales/en.json

@@ -167,7 +167,23 @@
     "manualTip": "Manual reminder — Claude never picks this up",
     "ctxMarkManual": "Mark as manual",
     "ctxMarkClaudeTask": "Mark as Claude task",
+    "ctxRefineTask": "Refine task",
+    "ctxPlanning": "Planning",
+    "ctxSchedule": "Schedule",
     "ctxDeleteTask": "Delete task",
+    "reasonAlreadyRunning": "Task is already running",
+    "reasonAlreadyQueued": "Already in the queue",
+    "reasonWaitingForReview": "Waiting for review",
+    "reasonSubtasksQueued": "Subtasks are already queued",
+    "reasonPlanNotFinalized": "Plan isn't finalized yet",
+    "reasonPlanningActive": "Planning session is active — finalize the plan first",
+    "reasonInteractiveSession": "An interactive session is open for this task",
+    "reasonNotRunning": "Task isn't running",
+    "reasonRefining": "Refine is already running",
+    "reasonNotIdle": "Only available for idle tasks",
+    "reasonIsPlanningParent": "Part of a plan",
+    "reasonIsChildTask": "Subtasks don't have their own planning session",
+    "reasonPlanAlreadyFinalized": "Plan is already finalized",
     "approve": "Approve",
     "approveTip": "Approve — mark Done",
     "reject": "Reject",