fix(docker): COPY favicon assets into image + cache header

Dockerfile selectively COPYs files into /usr/share/nginx/html. Favicon
assets (favicon.svg, favicon-32.png, favicon.ico, apple-touch-icon.png)
were added to the repo in ef31fb3 but never wired into the Dockerfile,
so a rebuilt container served 404 for /favicon.svg and friends — broken
favicon in prod even after `docker compose up -d --build`.

nginx.conf gets a matching long-cache rule for icon/image assets
(30 days, immutable, access_log off) — they rarely change and the file
name is the cache key anyway.

Deploy: on the VPS, `docker compose up -d --build`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -13,6 +13,7 @@ RUN rm -rf ./*
 COPY index.html ./
 COPY CV_Bastien_Chanot.html ./
 COPY CV_Bastien_Chanot.pdf ./
+COPY favicon.svg favicon-32.png favicon.ico apple-touch-icon.png ./
 
 # Non-root hardening: nginx:alpine already drops privileges to "nginx" user
 # for worker processes. Master runs as root only to bind port 80 inside