fix(ui): open saved plans against their owning project

Saved Project knowledge plans opened as an empty editor whenever the
viewer could not resolve the owning project from the current directory:
managed chats (openchamber:chats is not a registered project), worktrees
outside the repo path, and plan tabs restored after a reload. Titles
still rendered because the list reads the manifest through the correct
owner.

- Thread the owner explicitly (savedProjectPlan = { projectRef, planId })
  from the panel, mobile surfaces, and persisted context tabs; PlanView
  no longer guesses the project.
- An unrecognized directory resolves to no owner instead of borrowing
  the active project's knowledge.
- Serialize plan writes per document (planSaveQueue) so close/switch
  within the autosave debounce no longer drops the last edits, saves
  cannot land out of order, and a recovered save clears the error banner.
- Send saved-plan contents inline in Improve/Implement prompts (they
  have no file path); disable those actions for managed-chat plans,
  which have no project directory to create a session in.
- Drop persisted plan tabs that carry an id without an owner rather than
  reopening them against a guessed project.

packages/ui/src/components/layout/ContextPanel.tsx

@@ -943,7 +943,12 @@ export const ContextPanel: React.FC = () => {
             : activeTab?.mode === 'notes'
                 ? <ProjectContextPanel />
         : activeTab?.mode === 'plan'
-            ? <React.Suspense fallback={null}><PlanView targetPath={activeTab.targetPath} projectPlanId={activeTab.projectPlanId} /></React.Suspense>
+            ? <React.Suspense fallback={null}><PlanView
+                targetPath={activeTab.targetPath}
+                savedProjectPlan={activeTab.projectPlanId && activeTab.projectPlanRef
+                  ? { projectRef: activeTab.projectPlanRef, planId: activeTab.projectPlanId }
+                  : null}
+              /></React.Suspense>
             : null;
 
   const browserTabs = React.useMemo(