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/bloom.sexp

@@ -1,10 +1,11 @@
 ;; Bloom effect - glow on bright areas
-;; @param intensity float [0, 2] default 0.5
-;; @param threshold int [0, 255] default 200
-;; @param radius int [1, 50] default 15
 
 (define-effect bloom
-  ((intensity 0.5) (threshold 200) (radius 15))
+  :params (
+    (intensity :type float :default 0.5 :range [0 2])
+    (threshold :type int :default 200 :range [0 255])
+    (radius :type int :default 15 :range [1 50])
+  )
   (let* ((bright (map-pixels frame
                    (lambda (x y c)
                      (if (> (luminance c) threshold)