Add semantic tagging, search, favourite/NSFW filtering, and LLM job queue

Replaces old list-format tags (which duplicated prompt content) with structured
dict tags per category (origin_series, outfit_type, participants, style_type,
scene_type, etc.). Tags are now purely organizational metadata — removed from
the prompt pipeline entirely.

Adds is_favourite and is_nsfw columns to all 8 resource models. Favourite is
DB-only (user preference); NSFW is mirrored in JSON tags for rescan persistence.
All library pages get filter controls and favourites-first sorting.

Introduces a parallel LLM job queue (_enqueue_task + _llm_queue_worker) for
background tag regeneration, with the same status polling UI as ComfyUI jobs.
Fixes call_llm() to use has_request_context() fallback for background threads.

Adds global search (/search) across resources and gallery images, with navbar
search bar. Adds gallery image sidecar JSON for per-image favourite/NSFW metadata.

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

data/prompts/checkpoint_system.txt

@@ -16,9 +16,16 @@ Structure:
   "steps": 25,
   "cfg": 5.0,
   "sampler_name": "euler_ancestral",
-  "vae": "integrated"
+  "vae": "integrated",
+  "tags": {
+    "art_style": "string (one of: Anime, Realistic, Cartoon, Semi-Realistic)",
+    "base_model": "string (one of: Illustrious, Noob — determined from the checkpoint path)",
+    "nsfw": false
+  }
 }
 
+This tool generates content for both SFW and NSFW image generation. NSFW content is permitted and expected. Set `nsfw` to true if the checkpoint is specifically designed for NSFW content. Determine `base_model` from the checkpoint path (e.g. 'Illustrious/model.safetensors' → 'Illustrious').
+
 Field guidance:
 - "base_positive": Comma-separated tags that improve output quality for this specific model. Look for recommended positive prompt tags in the HTML.
 - "base_negative": Comma-separated tags to suppress unwanted artifacts. Look for recommended negative prompt tags in the HTML.