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/neon_glow.sexp

@@ -1,13 +1,13 @@
 ;; Neon Glow effect - glowing edge effect
-;; @param edge_low int [10, 200] default 50
-;; @param edge_high int [50, 300] default 150
-;; @param glow_radius int [1, 50] default 15
-;; @param glow_intensity float [0.5, 5] default 2
-;; @param background float [0, 1] default 0.3
 
 (define-effect neon_glow
-  ((edge_low 50) (edge_high 150) (glow_radius 15)
-   (glow_intensity 2) (background 0.3))
+  :params (
+    (edge_low :type int :default 50 :range [10 200])
+    (edge_high :type int :default 150 :range [50 300])
+    (glow_radius :type int :default 15 :range [1 50])
+    (glow_intensity :type int :default 2 :range [0.5 5])
+    (background :type float :default 0.3 :range [0 1])
+  )
   (let* ((edge-img (edges frame edge_low edge_high))
          (glow (blur edge-img glow_radius))
          ;; Intensify the glow