1.4.0 - Reverse Proxy support

FilaBridge can now live behind a path-prefixed reverse proxy, if that's your preferred way of doing things.

Reverse proxy paths

• You can now serve FilaBridge under a path prefix instead of at the root of
  a hostname. Set FILABRIDGE_BASE_PATH to the path your browser sees, for
  example /filabridge, and the interface, static assets, API, WebSocket and
  NFC endpoints all move with it. The setting is optional and defaults to
  the old behavior, so if you leave it alone nothing changes. A leading slash
  is optional and a trailing slash is ignored, matching how Spoolman's own
  SPOOLMAN_BASE_PATH works for consistency. Your proxy needs to pass
  the prefix through, or add it back before requests reach FilaBridge if it strips
  it. Thanks to @nebhale for building this! (#51)

• The healthcheck stays available at /healthz on the root no matter what
  prefix you set, so the healthcheck baked into the Docker image keeps working
  and you do not need to touch your compose file.

Changed

• Generated NFC and QR tag URLs now follow X-Forwarded-Host and
  X-Forwarded-Proto. Until now they were always built as http:// plus
  whatever host FilaBridge itself saw, which is the internal address when it
  sits behind a proxy. If you already run FilaBridge behind one, tags you
  generate from here on will carry your browser-visible hostname, and https
  where that applies. Tags you have already written are untouched. If your
  external hostname is not reachable from the network where you scan tags,
  you should configure your proxy not to send those two headers and you will
  get the old behavior back.

Other

• Refreshed the README screenshots and added one of the print history view.

Bambu Lab (still experimental, developer mode only), nothing new here.

The known issues listed under v1.3.0 still apply, positional AMS slot mapping
and first-plate-only numbers on multi-plate projects in particular. If you have
a Bambu printer with an AMS attached, running -bambu-probe and sending
me the output is still the most useful thing you can do to help. AMS support is
the last piece blocking a wider Bambu release. (However my own X2D with AMS is
due to arrive this week so I'll unblock myself sooner or later there!)