Build HistoryStore — opt-in git and mode detection

The pro-m1 foundation card. SwiftGitX 0.4.0 (bundled libgit2, the
pathfinder's pin) joins the one target; new Kanban/Git/ holds
BoardGitMode (pure nearest-.git-wins detection, .git-as-file counts,
NSString ancestor walk), HistoryStore (@MainActor @Observable;
compose() is the tier gate — free tier gets no object, no detection,
no stat), GitRepository (scope-confined SwiftGitX handles: create =
init + HEAD forced to main + whole-tree "Initial board state" commit;
branch reads incl. unborn/detached; path-history ranks), GitIdentity
(derived default as a pure function + repo-local config reader — not
libgit2's merged ladder), and GitPathHistory (Mutex-guarded lazy
ranker). beginSession composes the git state beside the tier and
feeds BoardStore.makeIdentityHistoryRanker; git-mode loads pass the
git-backed IdentityHistoryRanker to BoardLoader. The popover's git
slot resolves a pure five-way matrix: free tier unchanged (absent /
BoardGitNote), Pro mode-aware — Add Git on mode none, honest prose on
repo-nested, read-only branch line on git. Provider binding
unchanged: both tiers still bind native until the undo/redo card.

42 new tests across 8 suites, all repositories built through bundled
libgit2; InertGitTests untouched and green. 2194 tests / 375 suites.

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

Kanban/App/BoardWindowHost.swift

@@ -283,10 +283,20 @@ struct BoardWindowHost: View {
         // 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.
+        //
+        // The tier and the git state come from the **session**, which `start()` began a moment ago,
+        // rather than from the entitlement or the disk: a board's popover must describe the board as
+        // it opened (12-editions.md ▸ The entitlement, "an open board finishes with the provider it
+        // composed"; 06-history-undo.md ▸ Rules, mode is an open-time fact). A `nil` session cannot
+        // happen on this path — `beginSession` precedes `configureWindow` — and reads as the free
+        // tier's posture, which is the harmless direction.
+        let session = appModel.session(for: ref)
         windowController.installTitlebarAccessory(
             boardInfoTitlebarAccessory(
                 store: store,
                 recents: appModel.styleRecents,
+                tier: session?.tier ?? .free,
+                git: session?.git,
                 presentation: boardInfo
             )
         )