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/lib/projectContextApi.ts

@@ -57,6 +57,17 @@ export interface ProjectRef {
   path: string;
 }
 
+/**
+ * A saved project plan plus the project that owns it, carried as one value so
+ * a viewer can never end up with a plan id whose owner it has to guess.
+ * PlanView resolves no owner on its own: the panel (or the persisted tab,
+ * or the mobile surface) that opened the plan knows the owner exactly.
+ */
+export interface SavedProjectPlanTarget {
+  projectRef: ProjectRef;
+  planId: string;
+}
+
 export const PROJECT_NOTE_BODY_MAX_LENGTH = 3000;
 export const PROJECT_TODO_TEXT_MAX_LENGTH = 120;