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/strobe.sexp

@@ -1,8 +1,9 @@
 ;; Strobe effect - holds frames for choppy look
-;; @param frame_rate float [1, 60] default 12
 
 (define-effect strobe
-  ((frame_rate 12))
+  :params (
+    (frame_rate :type int :default 12 :range [1 60])
+  )
   (let* ((held (state-get 'held nil))
          (held-until (state-get 'held-until 0))
          (frame-duration (/ 1 frame_rate)))