Refactor UI, settings, and code quality across all categories

- Fix Replace Cover: routes now read preview_path from form POST instead of session (session writes from background threads were lost)
- Fix batch generation: submit all jobs immediately, poll all in parallel via Promise.all
- Fix label NameError in character generate route
- Fix style detail missing characters context
- Selected Preview pane: click any image to select it; data-preview-path on all images across all 8 detail templates
- Gallery → Library rename across all index page headings and navbar
- Settings: add configurable LoRA/checkpoint directories; default checkpoint selector moved from navbar to settings page
- Consolidate 6 get_available_*_loras() into single get_available_loras(category) reading from Settings
- ComfyUI tooltip shows currently loaded checkpoint name
- Remove navbar checkpoint bar
- Phase 4 cleanup: remove dead _queue_generation(), add session.modified, standardize log prefixes, rename action_type → action

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

models.py

@@ -132,6 +132,15 @@ class Settings(db.Model):
     openrouter_model = db.Column(db.String(100), default='google/gemini-2.0-flash-001')
     local_base_url = db.Column(db.String(255), nullable=True)
     local_model = db.Column(db.String(100), nullable=True)
+    # LoRA directories (absolute paths on disk)
+    lora_dir_characters = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Looks')
+    lora_dir_outfits    = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Clothing')
+    lora_dir_actions    = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Poses')
+    lora_dir_styles     = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Styles')
+    lora_dir_scenes     = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Backgrounds')
+    lora_dir_detailers  = db.Column(db.String(500), default='/ImageModels/lora/Illustrious/Detailers')
+    # Checkpoint scan directories (comma-separated list of absolute paths)
+    checkpoint_dirs     = db.Column(db.String(1000), default='/ImageModels/Stable-diffusion/Illustrious,/ImageModels/Stable-diffusion/Noob')
 
     def __repr__(self):
         return '<Settings>'