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/wave.sexp

@@ -1,11 +1,12 @@
 ;; Wave effect - sine wave displacement distortion
-;; @param amplitude float [0, 100] default 10
-;; @param wavelength float [10, 500] default 50
-;; @param speed float [0, 10] default 1
-;; @param direction string default "horizontal"
 
 (define-effect wave
-  ((amplitude 10) (wavelength 50) (speed 1) (direction "horizontal"))
+  :params (
+    (amplitude :type int :default 10 :range [0 100])
+    (wavelength :type int :default 50 :range [10 500])
+    (speed :type int :default 1 :range [0 10])
+    (direction :type string :default "horizontal")
+  )
   (let* ((w (width frame))
          (h (height frame))
          ;; Use _time for animation phase