Add composable ASCII art with per-cell effects and explicit effect loading

Implements ascii_fx_zone effect that allows applying arbitrary sexp effects
to each character cell via cell_effect lambdas. Each cell is rendered as a
small image that effects can operate on.

Key changes:
- New ascii_fx_zone effect with cell_effect parameter for per-cell transforms
- Zone context (row, col, lum, sat, hue, etc.) available in cell_effect lambdas
- Effects are now loaded explicitly from recipe declarations, not auto-loaded
- Added effects_registry to plan for explicit effect dependency tracking
- Updated effect definition syntax across all sexp effects
- New run_staged.py for executing staged recipes
- Example recipes demonstrating alternating rotation and blur/rgb_split patterns

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

sexp_effects/effects/color-adjust.sexp

@@ -1,8 +1,11 @@
 ;; Color adjustment effect - replaces TRANSFORM node
-;; Params: brightness (-255 to 255), contrast (0 to 3+), saturation (0 to 2+)
 
 (define-effect color-adjust
-  ((brightness 0) (contrast 1) (saturation 1))
+  :params (
+    (brightness :type int :default 0 :range [-255 255] :desc "Brightness adjustment")
+    (contrast :type float :default 1 :range [0 3] :desc "Contrast multiplier")
+    (saturation :type float :default 1 :range [0 2] :desc "Saturation multiplier")
+  )
   (-> frame
       (adjust :brightness brightness :contrast contrast)
       (shift-hsv :s saturation)))