add CSP-clean static build, hardened nginx config, and container image

nginx/security-headers.conf

@@ -0,0 +1,19 @@
+# Shared security headers. `include`d in the server block AND in every location that
+# sets its own add_header — a location-level add_header REPLACES inherited headers
+# rather than merging them (the classic nginx footgun).
+#
+# HSTS is host-scoped: NO includeSubDomains / preload, because the *.bztmon.com
+# wildcard points elsewhere and forcing HTTPS estate-wide from here would be reckless.
+# HTTP->HTTPS upgrade is Cloudflare's job.
+add_header Strict-Transport-Security "max-age=31536000" always;
+
+# script-src 'self' with NO 'unsafe-inline'. build.sh externalises every script and
+# hard-fails if an inline <script> reaches dist/, so this holds without an exception.
+# style-src needs 'unsafe-inline': GSAP animates by writing inline style attributes.
+add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; font-src 'self'; connect-src 'self'; worker-src 'self'; manifest-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'; frame-ancestors 'none'; upgrade-insecure-requests" always;
+add_header X-Content-Type-Options "nosniff" always;
+add_header X-Frame-Options "DENY" always;
+add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+add_header Permissions-Policy "camera=(), microphone=(), geolocation=(), payment=(), usb=(), interest-cohort=()" always;
+add_header Cross-Origin-Opener-Policy "same-origin" always;
+add_header Cross-Origin-Resource-Policy "same-origin" always;