Add stegasoo-api AUR package

New package in aur-api/ for API-only installation:
- Installs [api,cli,compression] extras
- Has fastapi/uvicorn for REST API
- No flask/gunicorn (web UI deps)
- 74MB package size
- Systemd service with TLS enabled by default

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

aur-api/test-build.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Test build the AUR API package locally
+
+set -e
+
+cd "$(dirname "$0")"
+
+echo "=== Cleaning previous builds ==="
+rm -rf stegasoo-api-git pkg src *.pkg.tar.zst *.whl 2>/dev/null || true
+
+echo "=== Generating .SRCINFO ==="
+makepkg --printsrcinfo > .SRCINFO
+
+echo "=== Building package ==="
+makepkg -sf
+
+echo "=== Package built ==="
+ls -la *.pkg.tar.zst
+
+echo ""
+echo "To install: sudo pacman -U stegasoo-api-git-*.pkg.tar.zst"
+echo "To test:    makepkg -si"