Add a public web front end alongside the CLI

Extracts the CLI pipeline into a reusable Pipeline class and exposes it
via a dependency-free JDK HttpServer (upload form, bounded worker pool
with 503 on overload, per-request size/time limits, no persisted
uploads), plus nginx/systemd deploy templates and Impressum/Datenschutz
placeholders for public operation.

Change-Id: I6e8e7afa3c4b1082cdf9e82da0fae0b5b49470ad
13 files changed