Remove the App Group wholesale — one sandbox, one bookmark, one flag

Phase 2 of the one-app pivot (DESIGN 12 ▸ App-side state, re-ruled
2026-07-30; reworks 566deab). AppGroup retires; what remains is
AppStateHome — ordinary sandbox Application Support as the one home for
the registry, clipboard staging and template stores, keeping the
unit-test-host redirect (the test host is the app and would sweep real
state). Scalar defaults return to UserDefaults.standard.

BoardRecord's per-edition grant slots and openNow flags collapse to one
bookmark + one isOpenNow; the legacy-key decode and adopt-in-memory
paths go (nothing shipped with group-era records), while the founding
four-keys-required / defaults-for-everything-since decode policy stays —
a bookmarkless record decodes as the born-orphan row rather than
quarantining the list. needsReopen and the pre-anchored re-grant panel
are removed whole: the only state that flow served — a record granted by
a sibling sandbox — is unrepresentable now, and a dead bookmark of our
own was already the orphan case by explicit comment. The
indexOfRecord path fallback dies with it; path is never a key again.

The cross-process freshness stamp (mtime+size re-read) and
BoardEditionPresence with its popover "Also open in…" line retire; the
clipboard prune keeps its atomic .sweeping/ claim-then-delete, reframed
for crash residue and open -n copies rather than sibling editions. The
application-groups entitlement key is gone.

1880 tests in 317 suites green (13 cross-edition tests retired with
their subject).

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/App/BoardWindowHost.swift

@@ -287,18 +287,7 @@ struct BoardWindowHost: View {
             boardInfoTitlebarAccessory(
                 store: store,
                 recents: appModel.styleRecents,
-                presentation: boardInfo,
-                // The cross-edition awareness line (12-editions.md ▸ Both editions installed), asked
-                // at each popover build rather than captured as a value: both facts behind it — the
-                // other edition's flag on the shared record, and whether that edition is still
-                // running — change while this window sits here, and neither is observable.
-                otherEditionNote: { [weak appModel] in
-                    guard let appModel else { return nil }
-                    return BoardEditionPresence.note(
-                        otherEditions: appModel.boardRegistry.otherEditionsFlaggedOpen(id: recordID),
-                        isRunning: BoardEditionPresence.isRunning
-                    )
-                }
+                presentation: boardInfo
             )
         )