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/pixelsort.sexp

@@ -1,10 +1,11 @@
 ;; Pixelsort effect - glitch art pixel sorting
-;; @param sort_by string default "lightness"
-;; @param threshold_low float [0, 255] default 50
-;; @param threshold_high float [0, 255] default 200
-;; @param angle float [0, 180] default 0
-;; @param reverse bool default false
 
 (define-effect pixelsort
-  ((sort_by "lightness") (threshold_low 50) (threshold_high 200) (angle 0) (reverse false))
+  :params (
+    (sort_by :type string :default "lightness")
+    (threshold_low :type int :default 50 :range [0 255])
+    (threshold_high :type int :default 200 :range [0 255])
+    (angle :type int :default 0 :range [0 180])
+    (reverse :type bool :default false)
+  )
   (pixelsort frame sort_by threshold_low threshold_high angle reverse))