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

KanbanTests/CardWindowShellTests.swift

@@ -43,7 +43,7 @@ private func subtitle(forCard cardID: String, boardNamed board: String, in model
     return CardWindowHost.subtitle(board: board, lane: placement.lane.title.value)
 }
 
-/// A registry whose file lives in temp rather than in the shared App Group container.
+/// A registry whose file lives in temp rather than in the app's real Application Support home.
 @MainActor
 private struct RegistryStorage {
     let folder: URL