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/resize-frame.sexp

@@ -1,7 +1,10 @@
 ;; Resize effect - replaces RESIZE node
-;; Params: width, height, mode (linear, nearest, area)
 ;; Note: uses target-w/target-h to avoid conflict with width/height primitives
 
 (define-effect resize-frame
-  ((target-w 640) (target-h 480) (mode "linear"))
+  :params (
+    (target-w :type int :default 640 :desc "Target width in pixels")
+    (target-h :type int :default 480 :desc "Target height in pixels")
+    (mode :type string :default "linear" :choices [linear nearest area] :desc "Interpolation mode")
+  )
   (resize frame target-w target-h mode))