Redesign: clear active nav state, Shipping labels + Receipts get free-text/raw print, shared label repository

- Home page is now just the print server overview, no more unrelated
  network links (3D printers, Cockpit) left over from when this was a
  general landing page.
- Navbar shows which section is active; Brother's per-printer buttons
  now live under a dedicated Brother nav item instead of always-visible.
- Shipping labels: paste raw ZPL directly (no need to save to a file
  first), with a Labelary preview link alongside it.
- Receipts: paste already-formatted ESC/POS text directly, printed as-is.
- Both can save what they just printed into a shared label repository
  (lib/label_repository.rb, one JSON file per label under data/labels/)
  for reprinting later -- saving happens independently of whether the
  print itself succeeds, so a failed/offline printer doesn't lose the
  content.

lib/label_repository.rb

@@ -0,0 +1,46 @@
+require 'json'
+require 'securerandom'
+require 'fileutils'
+
+# Simple file-backed store for reusable ZPL/ESC-POS label templates -- one
+# JSON file per label under DIR, similar in spirit to brother_ql_web's own
+# label repository. No per-printer targeting yet (type just says which print
+# path to use); that can be added once labels can target any of the five
+# printers via the Brother API.
+class LabelRepository
+  def initialize(dir)
+    @dir = dir
+    FileUtils.mkdir_p(@dir)
+  end
+
+  # type: "zpl" or "escpos"
+  def all(type: nil)
+    Dir.glob(File.join(@dir, '*.json')).map { |f| JSON.parse(File.read(f)) }
+       .select { |l| type.nil? || l['type'] == type }
+       .sort_by { |l| l['name'].downcase }
+  end
+
+  def find(id)
+    path = path_for(id)
+    return nil unless File.exist?(path)
+
+    JSON.parse(File.read(path))
+  end
+
+  def save(name:, type:, content:)
+    id = SecureRandom.uuid
+    label = { 'id' => id, 'name' => name, 'type' => type, 'content' => content }
+    File.write(path_for(id), JSON.generate(label))
+    label
+  end
+
+  def delete(id)
+    File.delete(path_for(id)) if File.exist?(path_for(id))
+  end
+
+  private
+
+  def path_for(id)
+    File.join(@dir, "#{id}.json")
+  end
+end