Add dither server

bin/dither/Gemfile

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+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "sinatra"
+gem "rackup"
+gem "mini_magick"

bin/dither/Gemfile.lock

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+GEM
+  remote: https://rubygems.org/
+  specs:
+    base64 (0.2.0)
+    mini_magick (4.12.0)
+    mustermann (3.0.0)
+      ruby2_keywords (~> 0.0.1)
+    rack (3.0.9)
+    rack-protection (4.0.0)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0, < 4)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
+    rackup (2.1.0)
+      rack (>= 3)
+      webrick (~> 1.8)
+    ruby2_keywords (0.0.5)
+    sinatra (4.0.0)
+      mustermann (~> 3.0)
+      rack (>= 3.0.0, < 4)
+      rack-protection (= 4.0.0)
+      rack-session (>= 2.0.0, < 3)
+      tilt (~> 2.0)
+    tilt (2.3.0)
+    webrick (1.8.1)
+
+PLATFORMS
+  arm64-darwin-22
+
+DEPENDENCIES
+  mini_magick
+  rackup
+  sinatra
+
+BUNDLED WITH
+   2.4.8

bin/dither/dither.rb

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+require "sinatra"
+require "mini_magick"
+
+MiniMagick.logger.level = Logger::DEBUG
+
+ROOT = ENV["ROOT"]
+KEY = ENV["KEY"]
+
+FileUtils.mkdir_p "tmp"
+
+get "/*" do |path|
+  filename = File.basename(path)
+  geometry = params["geo"]
+
+  @decrypted = Tempfile.new(filename, "tmp")
+  @dithered = Tempfile.new([filename, ".png"], "tmp")
+
+  %x(
+    openssl \
+      aes-256-cbc \
+      -d \
+      -in #{ROOT}/#{path}.enc \
+      -out #{@decrypted.path} \
+      -pass file:#{KEY} \
+      -iter 1000000
+  )
+
+  MiniMagick::Tool::Magick.new do |magick|
+    magick << @decrypted.path
+    magick.resize "#{geometry}^"
+    magick.gravity "center"
+    magick.extent geometry
+    magick.ordered_dither "o8x8"
+    magick.monochrome
+    magick << @dithered.path
+  end
+
+  content_type "image/png"
+  File.open(@dithered.path)
+end