Build the board popover — title widget, rename, styling, git slot

The window-title widget arrives as a leading titlebar accessory — a
quiet chevron on board windows only, installed and removed by the
window controller's own attach lifecycle — anchoring the one
board-level surface as a transient popover (the board window
deliberately grows no toolbar item for it). Inside: board rename
editing frontmatter title only (the folder is never renamed; an empty
commit removes the key and the window title falls back to the folder
name), the embedded shared style editor permanently targeting the
board, and the labeled Git section that this milestone only reserves
— a mode-none explanation and a disabled stub where m7's add-git,
branch, remote, and authentication controls land. Cmd-I (File >
Board Info) toggles it per window through a focused scene value,
kept apart from board-scoped transient state since a titlebar
popover belongs to one window, not to the board. Escape reverts a
dirty rename field and falls through to dismiss otherwise; a foreign
rename resyncs the field only while unfocused. 12 new tests.

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

Kanban/App/BoardWindowHost.swift

@@ -33,6 +33,12 @@ struct BoardWindowHost: View {
     /// alive for exactly as long as this window exists.
     @State private var windowController = HostedWindowController()
 
+    /// This window's board popover, open or not (03-board-ui.md § Board popover). `@State` for the
+    /// window controller's reason — one per window, living exactly as long as the window — which is
+    /// also what makes ⌘I mean "the board in front" rather than "some board": the flag reaches the
+    /// menu item through the focus system, like the store.
+    @State private var boardInfo = BoardInfoPresentation()
+
     @State private var phase: Phase = .opening
 
     private enum Phase {
@@ -79,8 +85,10 @@ struct BoardWindowHost: View {
                     }
                 )
             }
-            // "The board in front", for the menu items that act on it (`LaneWidthCommands`).
+            // "The board in front", for the menu items that act on it (`LaneWidthCommands`), and
+            // beside it the window's own popover flag, which is what File ▸ Board Info toggles.
             .focusedSceneValue(\.boardStore, store)
+            .focusedSceneValue(\.boardInfo, boardInfo)
         }
     }
 
@@ -123,16 +131,16 @@ struct BoardWindowHost: View {
         appModel.beginSession(ref: ref, store: store, recordID: recordID, access: access)
         phase = .open(store)
 
-        configureWindow(recordID: recordID)
+        configureWindow(store: store, recordID: recordID)
 
         // "Opening a board from welcome closes welcome" (02 § Launch and window lifecycle). Harmless
         // when welcome is not open, which is the ordinary case.
         dismissWindow(id: WindowID.welcome)
     }
 
-    /// Wires the window: the saved frame on the way in, frame changes on the way back out, and the
-    /// close interception that makes the flush unavoidable.
-    private func configureWindow(recordID: UUID) {
+    /// Wires the window: the saved frame on the way in, frame changes on the way back out, the
+    /// close interception that makes the flush unavoidable, and the title-bar widget.
+    private func configureWindow(store: BoardStore, recordID: UUID) {
         windowController.onAttach = { window in
             guard let saved = appModel.boardRegistry.record(id: recordID)?.windowFrame else { return }
             window.setFrame(HostedWindowController.placementOnCurrentScreens(for: saved), display: true)
@@ -157,6 +165,15 @@ struct BoardWindowHost: View {
                 windowController.closeAfterFlush()
             }
         }
+
+        // The window-title widget (03-board-ui.md § Board popover) — **board windows only**, which
+        // is why it is installed here rather than in `WindowAccessor`: welcome, the bootstrap and
+        // card windows share that machinery and have no board to describe. It goes in after the
+        // load rather than at attach because it carries the store; the controller installs it once,
+        // whichever of the two arrives second.
+        windowController.installTitlebarAccessory(
+            boardInfoTitlebarAccessory(store: store, recents: appModel.styleRecents, presentation: boardInfo)
+        )
     }
 
     // MARK: - Closing