feat(config-toggle): adaptive width, centering, and resize handling

Panel now selects from four width tiers based on $COLUMNS (with a 6-col
buffer per side before stepping up): 52-wide (default), 70, 74, or 78.
Each tier carries richer category descriptions sized to fit the layout.
The box is horizontally centered on every draw via a left-padding prefix.

Key reader switches from stty min 1 to min 0 / time 3, giving a 0.3 s
poll interval so COLUMNS changes are detected without a keypress. The
erase formula is now wrap-aware: prev_max_line_width / COLUMNS gives the
wrap factor, ensuring old wider panels are fully cleared after narrowing.
Idle timeout ticks that detect no resize are skipped entirely.

docs/fish-config.md

@@ -1246,10 +1246,10 @@ Add -i (interactive confirmation) to destructive commands:
 
     Synopsis:  config-toggle [-h]
 
-    Opens an interactive full-screen TUI for toggling the six opinionated
-    component categories (C1–C6) and the master disable variable without
-    having to type or remember variable names. Two scope tabs allow
-    independent per-scope configuration:
+    Opens an interactive TUI for toggling the six opinionated component
+    categories (C1–C6) and the master disable variable without having to
+    type or remember variable names. Two scope tabs allow independent
+    per-scope configuration:
 
       Universal — persists across all sessions (set -U)
       Session   — current shell only (set -g)
@@ -1257,6 +1257,16 @@ Add -i (interactive confirmation) to destructive commands:
     Changes apply immediately on each value keypress. Always available
     regardless of the __fish_config_opinionated master state.
 
+    The panel adapts to the terminal width automatically, selecting from
+    four layout tiers (with a 6-column buffer on each side before stepping
+    up to the next tier) and horizontally centering the box. The panel
+    redraws within ~0.3 s of a terminal resize with no keypress required.
+
+      COLUMNS >= 90  →  78-wide panel (most detail)
+      COLUMNS >= 86  →  74-wide panel
+      COLUMNS >= 82  →  70-wide panel
+      COLUMNS  < 82  →  52-wide panel (default)
+
     Navigation:
       ↑ ↓ / k j   Move cursor
       ← → / h l   Set value: OFF ← DEFAULT → ON (clamped)