Scope git history to current diagram by default

- History panel defaults to "This diagram" / "All" toggle
- "This diagram" filters git log to commits that touched only that
  diagram's JSON file (git log -- diagrams/0001_*.json)
- Automatically switches to "All" when no diagram is open
- Restore flow still works per-commit, per-file

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/js/app.js

@@ -2024,8 +2024,26 @@ class WiringApp {
       commitBtn._gitBound = true;
       commitBtn.addEventListener("click", () => this._gitCommit());
       document.getElementById("btn-git-push").addEventListener("click", () => this._gitPush());
+
+      // History scope toggle
+      const btnDiagram = document.getElementById("btn-git-log-diagram");
+      const btnAll     = document.getElementById("btn-git-log-all");
+      btnDiagram.addEventListener("click", () => {
+        btnDiagram.classList.add("active"); btnAll.classList.remove("active");
+        this._gitLoadLog();
+      });
+      btnAll.addEventListener("click", () => {
+        btnAll.classList.add("active"); btnDiagram.classList.remove("active");
+        this._gitLoadLog();
+      });
     }
 
+    // Default scope: "this diagram" if one is open, else "all"
+    const hasDiagram = !!this.diagramId;
+    document.getElementById("btn-git-log-diagram").classList.toggle("active", hasDiagram);
+    document.getElementById("btn-git-log-all").classList.toggle("active", !hasDiagram);
+    document.getElementById("btn-git-log-diagram").disabled = !hasDiagram;
+
     await this._gitRefresh();
   }
 
@@ -2051,9 +2069,13 @@ class WiringApp {
   async _gitLoadLog() {
     const list = document.getElementById("git-log-list");
     if (!list) return;
+    const diagramScope = document.getElementById("btn-git-log-diagram")?.classList.contains("active");
+    const diagramId = diagramScope && this.diagramId ? this.diagramId : null;
+    const title = document.getElementById("git-log-title");
+    if (title) title.textContent = diagramId ? "History — this diagram" : "History — all commits";
     list.innerHTML = '<div style="color:#556;padding:4px">Loading…</div>';
     try {
-      const entries = await api.git.log();
+      const entries = await api.git.log(diagramId);
       if (!entries.length) {
         list.innerHTML = '<div style="color:#556;padding:4px">No commits yet</div>';
         return;