Implement background exclusion and refactor folder structure

- Added configurable background exclusion (#1f2937) with tolerance
- Implemented alpha thresholding (>= 128) to eliminate edge artifacts
- Refactored folder structure into analyses/[slug]/images, settings, and results
- Updated pattern puller to skip existing images and handle network errors
- Updated .gitignore and automated tests for path integrity

app/lang/de.toml

@@ -12,6 +12,7 @@
 "toolbar.toggle_theme" = "Theme umschalten"
 "toolbar.open_app_folder" = "Programmordner öffnen"
 "toolbar.prefer_dark" = "Dunkelheit bevorzugen"
+"toolbar.exclude_bg" = "Hintergrund ausblenden ({color})"
 "status.no_file" = "Keine Datei geladen."
 "status.defaults_restored" = "Standardwerte aktiv."
 "status.free_draw_enabled" = "Freihand-Ausschluss aktiviert."

app/lang/en.toml

@@ -12,6 +12,7 @@
 "toolbar.toggle_theme" = "Toggle theme"
 "toolbar.open_app_folder" = "Open application folder"
 "toolbar.prefer_dark" = "Prefer darkness"
+"toolbar.exclude_bg" = "Exclude Background ({color})"
 "status.no_file" = "No file loaded."
 "status.defaults_restored" = "Defaults restored."
 "status.free_draw_enabled" = "Free-draw exclusion mode enabled."