feat(badges): configurable header bottom border and padding per template

Replaces hardcoded border-bottom/padding-bottom on badge_header div with
cfg_json fields: header_border_color, header_border_width, header_padding_bottom.
Empty color = no border. Template form exposes all three in Header & Branding.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/ae_events/types/ae_badge_template_cfg.ts

@@ -39,10 +39,19 @@ export interface BadgeTemplateCfg {
     // Header image vertical offset. CSS length applied as margin-top on the badge_header div.
     // Default (unset) = "2rem" (matches the prior hardcoded mt-8).
     // Negative values shift the image toward the top edge; larger values push it down.
-    // Useful when a background image's designed zone doesn't align with the default position.
     // Any CSS length works: "-0.5in", "1rem", "8px".
     header_margin_top?: string;
 
+    // Border drawn below the badge header image. Set header_border_color to enable.
+    // Unset = no border (default). Any valid CSS hex color.
+    header_border_color?: string;
+    // Thickness of the header bottom border. Any CSS length. Default "2px" when color is set.
+    header_border_width?: string;
+    // Padding below the header image (inside the badge_header div, above the border).
+    // Useful for creating visual space between the image and the body.
+    // Any CSS length: "0.5in", "1rem". Unset = no extra padding.
+    header_padding_bottom?: string;
+
     // Allow arbitrary extra keys to preserve forward-compatibility.
     [key: string]: any;
 }