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/datamosh.sexp

@@ -1,11 +1,12 @@
 ;; Datamosh effect - glitch block corruption
-;; @param block_size int [8, 128] default 32
-;; @param corruption float [0, 1] default 0.3
-;; @param max_offset int [0, 200] default 50
-;; @param color_corrupt bool default true
 
 (define-effect datamosh
-  ((block_size 32) (corruption 0.3) (max_offset 50) (color_corrupt true))
+  :params (
+    (block_size :type int :default 32 :range [8 128])
+    (corruption :type float :default 0.3 :range [0 1])
+    (max_offset :type int :default 50 :range [0 200])
+    (color_corrupt :type bool :default true)
+  )
   ;; Get previous frame from state, or use current frame if none
   (let ((prev (state-get "prev_frame" frame)))
     (begin