Separate face detection into standalone daemon

- Strip all face code from update.rb; add shared log helper writing to
  /opt/albumen/log/albumen.log with [update] prefix.  update.rb now owns
  only album.json; face_daemon.rb owns faces.json.
- New scripts/face_daemon.rb: polls MEDIA_ROOT for unprocessed images,
  calls faces.py in batches, writes per-directory faces.json sidecars
  atomically.  Graceful SIGTERM/SIGINT shutdown between directories.
- New config/face_daemon.service: systemd unit running as albumen user,
  Restart=on-failure, logs via SyslogIdentifier=albumen-faces.
- app.rb: add FACES_ENABLED constant; load_faces() helper reads faces.json;
  album_files() merges face data into each entry as :faces field.
- Update README.md and DESIGN.md to document the new daemon architecture,
  faces.json schema, and service management commands.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/app.rb b/app.rb
index 6b11d5d..a923b4d 100644
--- a/app.rb
+++ b/app.rb
@@ -23,7 +23,8 @@ VIDEO_EXTS = %w[mp4 mov avi mkv webm m4v ogv].freeze
 AUDIO_EXTS = %w[mp3 flac ogg wav m4a aac].freeze
 MEDIA_EXTS = (IMAGE_EXTS + VIDEO_EXTS + AUDIO_EXTS).freeze
 
-APP_CONFIG = (File.exist?(CONFIG_PATH) ? YAML.load_file(CONFIG_PATH, symbolize_names: true) : {}).freeze
+APP_CONFIG     = (File.exist?(CONFIG_PATH) ? YAML.load_file(CONFIG_PATH, symbolize_names: true) : {}).freeze
+FACES_ENABLED  = (APP_CONFIG.dig(:faces, :enabled) == true).freeze
 
 # ── Sinatra config ─────────────────────────────────────────────────────────────
 
@@ -83,7 +84,17 @@ helpers do
     { 'files' => {}, 'visible' => true }
   end
 
+  def load_faces(dir)
+    path = File.join(dir, 'faces.json')
+    return {} unless File.exist?(path)
+    JSON.parse(File.read(path))
+  rescue JSON::ParserError
+    {}
+  end
+
   def album_files(dir, data)
+    face_data = FACES_ENABLED ? load_faces(dir) : {}
+
     files = Dir.children(dir)
                .sort
                .select { |n| MEDIA_EXTS.include?(File.extname(n).downcase.delete_prefix('.')) }
@@ -107,6 +118,7 @@ helpers do
         shutter:       meta['shutter'],
         iso:           meta['iso'],
         transcoded_to: meta['transcoded_to'],
+        faces:         face_data[name],
       }
     end