Refactor: Extract banner template to shared banner.sh

- Create rpi/banner.sh with print_banner, print_gradient_line,
  print_logo, print_starfield, print_complete_banner functions
- Update setup.sh to source banner.sh (with inline fallback for curl)
- Update first-boot-wizard.sh to use banner functions
- Update sanitize-for-image.sh to use banner functions
- Fix MOTD thermometer spacing alignment

Single source of truth for ASCII banner styling.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/banner.sh

@@ -0,0 +1,63 @@
+#!/bin/bash
+# Stegasoo Banner/Header Template
+# Source this file to use the banner functions
+#
+# Usage:
+#   source "$(dirname "${BASH_SOURCE[0]}")/banner.sh"
+#   print_banner "Raspberry Pi Setup"
+#   print_gradient_line
+
+# Colors
+STEGASOO_GOLD='\033[38;5;220m'
+STEGASOO_GRAY='\033[0;90m'
+STEGASOO_WHITE='\033[1;37m'
+STEGASOO_GREEN='\033[0;32m'
+STEGASOO_NC='\033[0m'
+
+# Gradient line (purple -> blue)
+print_gradient_line() {
+    echo -e "\033[38;5;93m══════════════\033[38;5;99m══════════════\033[38;5;105m══════════════\033[38;5;117m══════════════\033[0m"
+}
+
+# Starfield decoration line
+print_starfield() {
+    echo -e "${STEGASOO_GRAY} · .  · .  *  · .  *  · .  *  · .  *  · .  *  · .  ·${STEGASOO_NC}"
+}
+
+# ASCII logo (gold)
+print_logo() {
+    echo -e "${STEGASOO_GOLD}    ___  _____  ___    ___    _    ___    ___    ___${STEGASOO_NC}"
+    echo -e "${STEGASOO_GOLD}   / __||_   _|| __|  / __|  /_\\  / __|  / _ \\  / _ \\\\${STEGASOO_NC}"
+    echo -e "${STEGASOO_GOLD}   \\__ \\  | |  | _|  | (_ | / _ \\ \\__ \\ | (_) || (_) |${STEGASOO_NC}"
+    echo -e "${STEGASOO_GOLD}   |___/  |_|  |___|  \\___//_/ \\_\\|___/  \\___/  \\___/${STEGASOO_NC}"
+}
+
+# Full banner with optional subtitle
+# Usage: print_banner "Subtitle Text"
+print_banner() {
+    local subtitle="$1"
+    echo ""
+    print_gradient_line
+    print_starfield
+    print_logo
+    print_starfield
+    print_gradient_line
+    if [ -n "$subtitle" ]; then
+        echo -e "${STEGASOO_WHITE}                    ${subtitle}${STEGASOO_NC}"
+        print_gradient_line
+    fi
+}
+
+# Completion banner (green title)
+# Usage: print_complete_banner "Setup Complete!"
+print_complete_banner() {
+    local title="$1"
+    echo ""
+    print_gradient_line
+    print_starfield
+    print_logo
+    print_starfield
+    print_gradient_line
+    echo -e "\033[1;32m                      ${title}\033[0m"
+    print_gradient_line
+}