fix org-caldav: use Basic auth with url-basic-auth-storage pre-registration

Baikal server is configured for Basic auth (dav_auth_type: Basic).
Previous Digest auth approach was wrong. New approach:
- my/caldav-preregister-basic-auth reads credentials from auth-source (~/.authinfo)
- Pre-registers in url-basic-auth-storage to bypass auth-source retries during requests
- Gives clear error if ~/.authinfo not configured
- Removed family calendar sync (was failing; can be added later)

config.el

@@ -1733,15 +1733,41 @@ current frame."
 ;;; --- Tier 1: High impact ---
 
 ;; org-caldav — CalDAV sync for org (Baikal, Basic auth over HTTPS)
-;; Add to ~/.authinfo:
+;; Add to ~/.authinfo (chmod 600):
 ;;   machine cal.apps.sukany.cz login martin password YOUR_PASSWORD
-;;   machine cal.apps.sukany.cz login family password YOUR_PASSWORD
 (use-package! org-caldav
   :commands my/org-caldav-sync
   :config
+  (defun my/caldav-preregister-basic-auth ()
+    "Read CalDAV credentials from auth-source and pre-register for Basic auth.
+This bypasses auth-source retry issues during CalDAV requests.
+Requires ~/.authinfo entry:
+  machine cal.apps.sukany.cz login martin password <pass>"
+    (require 'url-auth)
+    (require 'auth-source)
+    (let* ((entry (car (auth-source-search
+                        :host "cal.apps.sukany.cz"
+                        :user "martin"
+                        :max 1
+                        :require '(:user :secret))))
+           (user   (when entry (plist-get entry :user)))
+           (secret (when entry (plist-get entry :secret)))
+           (pass   (when secret (if (functionp secret) (funcall secret) secret))))
+      (if (and user pass)
+          (progn
+            ;; Pre-register in url-basic-auth-storage: (server realm user pass)
+            (setq url-basic-auth-storage
+                  (cl-remove "cal.apps.sukany.cz" url-basic-auth-storage
+                             :key #'car :test #'equal))
+            (push (list "cal.apps.sukany.cz" "BaikalDAV" user pass)
+                  url-basic-auth-storage)
+            t)
+        (user-error "CalDAV: no credentials found.\nAdd to ~/.authinfo:\n  machine cal.apps.sukany.cz login martin password <pass>"))))
+
   (defun my/org-caldav-sync ()
     "Sync org-caldav: personal calendar (twoway) + family calendar (read-only)."
     (interactive)
+    (my/caldav-preregister-basic-auth)
     ;; Personal calendar — twoway, new events created here
     (setq org-caldav-url           "https://cal.apps.sukany.cz/dav.php/calendars/martin"
           org-caldav-calendar-id   "default"
@@ -1749,14 +1775,7 @@ current frame."
           org-caldav-files         '("~/org/personal.org" "~/org/work.org")
           org-caldav-sync-direction 'twoway)
     (org-caldav-sync)
-    ;; Family calendar — read-only (fromcal), no writes back
+    (message "CalDAV sync complete: personal (twoway)")))
-    (setq org-caldav-url           "https://cal.apps.sukany.cz/dav.php/calendars/family"
-          org-caldav-calendar-id   "default"
-          org-caldav-inbox         "~/org/family-calendar.org"
-          org-caldav-files         nil
-          org-caldav-sync-direction 'fromcal)
-    (org-caldav-sync)
-    (message "CalDAV sync complete: personal (twoway) + family (read-only)")))
 
 (map! :leader "o c" #'my/org-caldav-sync)