add flashcard generation tooling and binary search cards

- gen-flashcards.py: auto-generate recognition cards from all problem files
- toolkit/gen-problem-cards.org: 199 auto-generated problem cards
- 5 binary search tool cards (std::binary_search, std::lower_bound, comparison, two-sum pattern, sorting gotcha)
- two-sum.org: add binary search C++ attempt
- lc-org.el: add doom emacs localleader keybinding support

org/study_deck_02/lc-org.el

@@ -71,22 +71,32 @@ Returns a plist (:problem :lang :input :code) or signals an error."
                    (display-buffer (process-buffer proc)))))
     (display-buffer buf)))
 
-(defvar lc-org-mode-map
-  (let ((map (make-sparse-keymap))
-        (prefix (make-sparse-keymap)))
+(defvar lc-org-mode-map (make-sparse-keymap)
+  "Keymap for `lc-org-mode'.")
+
+(when (and (boundp 'doom-version) (fboundp 'map!))
+  (map! :map lc-org-mode-map
+        :localleader
+        :prefix "l"
+        "s" #'lc-org-submit
+        "r" #'lc-org-run
+        "t" #'lc-org-status
+        "p" #'lc-org-show-problem
+        "d" #'lc-org-daily))
+
+(unless (and (boundp 'doom-version) (fboundp 'map!))
+  (let ((prefix (make-sparse-keymap)))
     (define-key prefix (kbd "s") #'lc-org-submit)
     (define-key prefix (kbd "r") #'lc-org-run)
     (define-key prefix (kbd "t") #'lc-org-status)
     (define-key prefix (kbd "p") #'lc-org-show-problem)
     (define-key prefix (kbd "d") #'lc-org-daily)
-    (define-key map (kbd "C-c l") prefix)
-    map)
-  "Keymap for `lc-org-mode'.")
+    (define-key lc-org-mode-map (kbd "C-c l") prefix)))
 
 ;;;###autoload
 (define-minor-mode lc-org-mode
   "Minor mode for LeetCode CLI integration in org source blocks.
-Keybindings under C-c l:
+Keybindings under localleader l (SPC m l or , l):
   s  submit   — submit current block
   r  run      — run with test input
   t  status   — check submission status