Add modular primitive libraries and fix Symbol class compatibility

- Add primitive_libs/ with modular primitive loading (core, math, image,
  color, color_ops, filters, geometry, drawing, blending, arrays, ascii)
- Effects now explicitly declare dependencies via (require-primitives "...")
- Convert ascii-fx-zone from hardcoded special form to loadable primitive
- Add _is_symbol/_is_keyword helpers for duck typing to support both
  sexp_effects.parser.Symbol and artdag.sexp.parser.Symbol classes
- Auto-inject _interp and _env for primitives that need them
- Remove silent error swallowing in cell_effect evaluation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

effects/ascii_alternating_rotate.sexp

@@ -6,6 +6,7 @@
 (recipe "ascii_alternating_rotate"
   :version "1.0"
   :description "ASCII art with alternating rotation directions per cell"
+  :minimal-primitives true
   :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
 
   :params (