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.

docs/open.md

@@ -78,6 +78,16 @@ Offene Entscheidungen dazu:
   lives as two new nullable columns directly on `TaskEntity` (not a phantom `WorktreeEntity` row),
   specifically so `list_worktrees`/the Worktrees overview never see it.
 
+- **Post-merge verify gate (2026-08-05)** — build + unit tests all green (incl. real-process
+  `VerifyCommandRunner` exit-code/output/timeout tests and `TaskMergeService` success/failure/
+  timeout paths via a fake runner), but **not visually verified**: open a list's Settings modal,
+  confirm the new "VERIFICATION" section renders below Agent with a settable/clearable
+  `VerifyCommand` field; approve a task on a list with a failing command configured and confirm
+  the footer/error surfacing (`ShowErrorAsync`) actually shows the verify failure message instead
+  of silently looking like nothing happened. Also no real-build smoke test (a real `dotnet build`/
+  `dotnet test` invocation as the configured command) — only fast synthetic commands (`exit N`,
+  `ping` for timeout) were exercised.
+
 ---
 
 ## Bewusst verworfen (nicht erneut vorschlagen)