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/outline.sexp

@@ -1,11 +1,12 @@
 ;; Outline effect - shows only edges
-;; @param thickness int [1, 10] default 2
-;; @param threshold int [20, 300] default 100
-;; @param color list default (0 0 0)
-;; @param fill_mode string default "original"
 
 (define-effect outline
-  ((thickness 2) (threshold 100) (color (list 0 0 0)) (fill_mode "original"))
+  :params (
+    (thickness :type int :default 2 :range [1 10])
+    (threshold :type int :default 100 :range [20 300])
+    (color :type list :default (list 0 0 0)
+  )
+  (fill_mode "original"))
   (let* ((edge-img (edges frame (/ threshold 2) threshold))
          (dilated (if (> thickness 1)
                       (dilate edge-img thickness)