feat: detached-runs monitor page (T3 parity)

New Runs sidebar destination listing detached invocations (detach:true)
with phase, current step, project and a Cancel button while
pending/running. Workspace-scoped like Audit/Approvals, polls every 2s.
Detached runs are opt-in (detached.enabled) — the empty state explains
how to enable them. Inline help doc DE+EN. DetachedRun model +
listDetachedRuns/cancelDetachedRun in HubService, backed by the SDK's
listInvocations()/cancelInvocation(). flutter analyze clean; 29 tests
green (sidebar Y-stability updated for the new destination, model
mapping unit-tested).

Screenshot verification (light+dark) deferred — shared desktop in use.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

CHANGELOG.md

@@ -5,6 +5,16 @@ version + `kStudioVersion` in `lib/main.dart` stay in lockstep.
 
 ## Unreleased
 
+### Added (detached-runs monitor — T3 parity)
+
+- **Runs page.** A new sidebar destination lists detached invocations
+  (submitted with `detach: true`) with their phase, current step,
+  project and a **Cancel** button while pending/running. Workspace-
+  scoped like Audit and Approvals; polls every 2 s. Detached runs are
+  opt-in (`detached.enabled`), so the empty state explains how to turn
+  them on. Inline help doc (DE+EN). Backed by the SDK's
+  `listInvocations()` + `cancelInvocation()`.
+
 ### Added (multi-project, stages ① + ②)
 
 - **Workspace switcher.** The Audit and Approvals AppBars carry a