feat(worker): add post-merge verification gate for list merges

Per-list optional VerifyCommand (list_config.verify_command) runs via
VerifyCommandRunner in the list's working dir right after a successful
merge/continue-merge, before the task is allowed to reach Done. A
non-zero exit or timeout leaves the merge in place but keeps the task
out of Done and reports StatusVerifyFailed with an output excerpt
through MergeResultDto/review_task; no command configured behaves
exactly as before. Merges against the same repo are now serialized
per working dir so a running verify can't be interrupted by a second
merge landing mid-build. Adds the field to the List Settings modal
(en/de localized) and covers success/failure/timeout in
TaskMergeServiceTests + VerifyCommandRunnerTests.

src/ClaudeDo.Localization/locales/en.json

@@ -326,7 +326,11 @@
       "manualList": "Manual list (reminders)",
       "manualListHint": "New tasks in this list start out manual: no queueing, running or refining, and automation skips them. You can still open a hand-driven session.",
       "sectionAgent": "AGENT",
-      "resetAgentSettings": "Reset agent settings"
+      "resetAgentSettings": "Reset agent settings",
+      "sectionVerify": "VERIFICATION",
+      "verifyCommand": "Verify command",
+      "verifyCommandPlaceholder": "(none — merge behaves as today)",
+      "verifyCommandHint": "Runs in the working directory after a merge lands, before the task is marked Done. A non-zero exit (or timeout) leaves the merge in place but keeps the task out of Done and reports the failure."
     },
     "merge": {
       "title": "MERGE WORKTREE",
@@ -550,6 +554,7 @@
     "worktreesTab": { "workerOffline": "Worker offline.", "removed": "Removed {0} worktree(s).", "blocked": "Cannot force-remove: {0} task(s) still running. Cancel them first.", "removedFrom": "Removed {0} worktree(s) from {1} task(s).", "cleanupFailed": "Cleanup failed: {0}", "resetFailed": "Reset failed: {0}" },
     "worktreesOverview": { "titleAll": "Worktrees", "titleList": "Worktrees — {0}", "listFallback": "list", "cleanupFailed": "Cleanup failed.", "cleanupFailedDetailed": "Cleanup failed: {0}", "removed": "Removed {0} worktree(s).", "discardFailed": "Failed to discard worktree.", "keepFailed": "Failed to keep worktree.", "cannotForceRunning": "Cannot force-remove a running task.", "forceRemoveFailed": "Force remove failed.", "forceRemoveFailedDetailed": "Force remove failed: {0}", "batchProgress": "Merging {0}/{1}…", "batchDone": "Merged {0}, {1} need resolution." },
     "listSettings": { "untitled": "Untitled" },
+    "detailsIsland": { "verifyFailed": "Merge landed, but the list's verify command failed — the task was kept out of Done." },
     "lists": { "localSuffix": "{0} / local", "smartMyDay": "My Day", "smartImportant": "Important", "smartPlanned": "Planned", "virtualQueue": "Queue", "virtualRunning": "Running", "virtualReview": "Review", "newList": "New list" }
   }
 }