fix(org-modern): vector star + GitHub recipe for latest version; feat: fullscreen on start

- packages.el: recipe pointing to minad/org-modern GitHub main
  (bypasses Doom lockfile pin, gets version with org-indent-mode star fix)
- config.el: org-modern-star as vector ["◉"] + org-modern-hide-stars
  (vector format works reliably; list format had activation timing issues)
- config.el: initial/default-frame-alist fullscreen maximized
  (Emacs starts maximized on every launch)

packages.el

@@ -81,7 +81,8 @@
 (package! olivetti)
 
 ;; Org enhancements
-(package! org-modern)
+(package! org-modern
+  :recipe (:host github :repo "minad/org-modern"))  ; pin to latest main, bypasses Doom lockfile
 (package! org-fragtog)
 (package! org-super-agenda)
 (package! org-noter)