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, 37 insertions, 0 deletions

diff --git a/tests/test-org-drill-custom-groups.el b/tests/test-org-drill-custom-groups.el
new file mode 100644
index 0000000..fe1e22c
--- /dev/null
+++ b/tests/test-org-drill-custom-groups.el
@@ -0,0 +1,37 @@
+;;; test-org-drill-custom-groups.el --- Customize sub-group structure  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The defcustoms are split across four sub-groups under the top-level
+;; org-drill group so M-x customize-group org-drill is navigable instead of
+;; dumping 37 options in one flat list.  (There is no leitner sub-group: the
+;; Leitner settings are defvars, not defcustoms.)
+
+;;; Code:
+
+(require 'ert)
+(require 'org-drill)
+
+(defconst test-org-drill-subgroups
+  '(org-drill-display org-drill-algorithm org-drill-session org-drill-leech)
+  "The customize sub-groups org-drill defines.")
+
+(ert-deftest test-org-drill-subgroups-exist-and-nest-under-org-drill ()
+  "Each sub-group is defined and is a child of the org-drill group."
+  (dolist (g test-org-drill-subgroups)
+    (should (get g 'group-documentation))
+    (should (assq g (get 'org-drill 'custom-group)))))
+
+(ert-deftest test-org-drill-defcustoms-land-in-expected-subgroups ()
+  "A representative defcustom from each sub-group is a member of it."
+  (should (assq 'org-drill-spaced-repetition-algorithm
+                (get 'org-drill-algorithm 'custom-group)))
+  (should (assq 'org-drill-leech-method
+                (get 'org-drill-leech 'custom-group)))
+  (should (assq 'org-drill-scope
+                (get 'org-drill-session 'custom-group)))
+  (should (assq 'org-drill-use-visible-cloze-face-p
+                (get 'org-drill-display 'custom-group))))
+
+(provide 'test-org-drill-custom-groups)
+
+;;; test-org-drill-custom-groups.el ends here