fix(tooling): star map 16:9 ratio, circular fade, trimmed margins

Canvas now 16:9 with circle filling height. Radial fade gradient uses
userSpaceOnUse for true circular shape. Hop 15+ folded into final ring.
Margins trimmed to fit content.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tooling/generate-star-map-svg.py

@@ -62,10 +62,6 @@ if folded_nodes:
 max_display_hop = FOLD_HOP
 
 # --- Layout parameters ---
-width, height = 3200, 3200
-cx, cy = width / 2, height / 2
-
-# Ring radii — hop 15+ gets a wider band
 RING_STEP = 55
 RING_BASE = 50
 ring_radius = {}
@@ -80,6 +76,12 @@ NORMAL_BAND = 27
 FOLD_BAND = NORMAL_BAND  # same width as normal rings
 FADE_BAND = NORMAL_BAND * 4  # empty fade zone beyond the last ring
 
+# Canvas: 16:9, circle fills the height
+_max_r = RING_STEP * FOLD_HOP + RING_BASE + NORMAL_BAND + FADE_BAND + 60
+height = int(_max_r * 2 + 120)
+width = int(height * 16 / 9)
+cx, cy = width / 2, height / 2
+
 # 90-degree wedges, no gaps, centered on cardinals
 sector_wedge_center = {
     'north_reach': -math.pi / 2,
@@ -227,12 +229,15 @@ svg = []
 svg.append(f'<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 {width} {height}" width="{width}" height="{height}">')
 
 # Defs for the fade gradient beyond the last ring
+# Use userSpaceOnUse so the gradient is a true circle regardless of canvas aspect ratio
 svg.append('<defs>')
-fade_start = ring_radius[FOLD_HOP] + FOLD_BAND  # outer edge of last ring
-fade_end = fade_start + FADE_BAND  # end of fade zone
-start_pct = fade_start / (width / 2) * 100
-end_pct = min(fade_end / (width / 2) * 100, 100)
-svg.append(f'<radialGradient id="fadeEdge" cx="50%" cy="50%" r="50%">')
+fade_start = ring_radius[FOLD_HOP] + FOLD_BAND
+fade_end = fade_start + FADE_BAND
+# Gradient radius must cover corners of canvas
+grad_r = max(width, height)
+start_pct = fade_start / grad_r * 100
+end_pct = fade_end / grad_r * 100
+svg.append(f'<radialGradient id="fadeEdge" cx="{cx}" cy="{cy}" r="{grad_r}" gradientUnits="userSpaceOnUse">')
 svg.append(f'  <stop offset="0%" stop-color="#0a0a1a" stop-opacity="0"/>')
 svg.append(f'  <stop offset="{start_pct:.1f}%" stop-color="#0a0a1a" stop-opacity="0"/>')
 svg.append(f'  <stop offset="{end_pct:.1f}%" stop-color="#0a0a1a" stop-opacity="1"/>')