fix(zsh): bind history-substring-search for CSI and SS3 arrows

historySubstringSearch bound only the default CSI sequences (^[[A/^[[B),
so Up/Down did nothing at the prompt in foot and iTerm2, which send the
SS3 application-mode sequences (^[OA/^[OB). Bind both forms via
searchUpKey/searchDownKey; this covers foot, iTerm2 and the Linux TTY
(CSI).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/shell.nix

@@ -6,7 +6,21 @@
     enableCompletion = true;
     enableVteIntegration = true;
     autosuggestion.enable = true;
-    historySubstringSearch.enable = true;
+    # Bind Up/Down for history-substring-search in BOTH cursor-key modes: CSI
+    # (^[[A/^[[B -- normal mode, and what the Linux TTY sends) and SS3
+    # (^[OA/^[OB -- application mode, used by foot, tmux and iTerm2). Binding
+    # only the default CSI form leaves it dead at the prompt in foot/iTerm2.
+    historySubstringSearch = {
+      enable = true;
+      searchUpKey = [
+        "^[[A"
+        "^[OA"
+      ];
+      searchDownKey = [
+        "^[[B"
+        "^[OB"
+      ];
+    };
     history.append = true;
     oh-my-zsh = {
       enable = true;