refactor: dedupe presenters, group defcustoms, and fill in docstrings

A cleanup pass over org-drill internals, squashed from the refactor/wave3-cleanup branch. No behavior change. Each step kept the existing tests green and added its own.

I shared two duplicated helpers across the language card getters: org-drill--read-property-string and org-drill--face-from-alist.

I factored the cloze body-scan out of the two multicloze presenters into org-drill--cloze-body-bounds, org-drill--count-cloze-matches, and org-drill--hide-cloze-by-index, so each presenter just picks which indices to hide.

I pulled the presenter resolution and the four-way result classification out of org-drill-entry-f into org-drill--resolve-presenter and org-drill--classify-presentation-result, untangling the pivot of every drill iteration.

I split the 37 defcustoms (and the three cloze faces) into four customize sub-groups (display, algorithm, session, leech) so customize-group org-drill is navigable. There's no leitner group because the Leitner settings are defvars.

I documented the 22 defuns that had no docstring, rewrote the corrupted org-drill-presentation-prompt-in-mini-buffer docstring, and switched eleven docstrings to the imperative "Return" (issue #2).

1 files changed, 18 insertions, 0 deletions

diff --git a/tests/test-org-drill-multicloze-hiding.el b/tests/test-org-drill-multicloze-hiding.el
index f67e083..b225008 100644
--- a/tests/test-org-drill-multicloze-hiding.el
+++ b/tests/test-org-drill-multicloze-hiding.el
@@ -158,6 +158,24 @@ Verified by checking the resulting overlay's bounds match the
      (org-drill-present-multicloze-hide-nth (org-drill-session) -1))
     (should (= 1 overlays-during-prompt))))
 
+;;;; org-drill--count-cloze-matches (extracted scan helper)
+
+(ert-deftest test-org-drill-count-cloze-matches-counts-body-clozes ()
+  "Counts each cloze region between the body bounds."
+  (with-cloze-card "* Question :drill:
+[A] [B] [C] [D]
+"
+    (let ((bounds (org-drill--cloze-body-bounds)))
+      (should (= 4 (org-drill--count-cloze-matches (car bounds) (cdr bounds)))))))
+
+(ert-deftest test-org-drill-count-cloze-matches-zero-when-no-cloze ()
+  "A body with no cloze syntax counts zero."
+  (with-cloze-card "* Question :drill:
+No cloze syntax here.
+"
+    (let ((bounds (org-drill--cloze-body-bounds)))
+      (should (= 0 (org-drill--count-cloze-matches (car bounds) (cdr bounds)))))))
+
 (provide 'test-org-drill-multicloze-hiding)
 
 ;;; test-org-drill-multicloze-hiding.el ends here