Add Checkpoints Gallery with per-checkpoint generation settings

- New Checkpoint model (slug, name, checkpoint_path, data JSON, image_path)
- sync_checkpoints() loads metadata from data/checkpoints/*.json and falls
  back to template defaults for models without a JSON file
- _apply_checkpoint_settings() applies per-checkpoint steps, CFG, sampler,
  base positive/negative prompts, and VAE (with dynamic VAELoader node
  injection for non-integrated VAEs) to the ComfyUI workflow
- Bulk Create from Checkpoints: scans Illustrious/Noob model directories,
  reads matching HTML files, uses LLM to populate metadata, falls back to
  template defaults when no HTML is present
- Gallery index with batch cover generation and WebSocket progress bar
- Detail page showing Generation Settings and Base Prompts cards
- Checkpoints nav link added to layout
- New data/prompts/checkpoint_system.txt LLM system prompt
- Updated README with all current galleries and file structure
- Also includes accumulated action/scene JSON updates, new actions, and
  other template/generator improvements from prior sessions

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

data/actions/4p_sex.json

@@ -2,34 +2,32 @@
   "action_id": "4p_sex",
   "action_name": "4P Sex",
   "action": {
-    "full_body": "complex group composition involving four subjects in close physical contact, bodies intertwined or overlapping in a cluster",
-    "head": "heads positioned close together, looking at each other or facing different directions, varied expressions",
-    "eyes": "open or half-closed, gazing at other subjects",
-    "arms": "arms reaching out, holding, or embracing other subjects in the group, creating a web of limbs",
-    "hands": "hands placed on others' bodies, grasping or touching",
-    "torso": "torsos leaning into each other, pressed together or arranged in a pile",
-    "pelvis": "pelvises positioned in close proximity, aligned with group arrangement",
-    "legs": "legs entangled, kneeling, lying down, or wrapped around others",
-    "feet": "feet resting on the ground or tucked in",
-    "additional": "high density composition, multiple angles of interaction, tangled arrangement of bodies"
-  },
-  "participants": {
-    "solo_focus": "false",
-    "orientation": "MFFF"
+    "full_body": "Choreographed foursome group sex scene involving four participants (e.g., 1 girl and 3 boys or 3 girls and 1 boy) engaged in simultaneous sexual acts like double penetration or cooperative fellatio.",
+    "head": "Moaning expression, open mouth, potentially heavily breathing or performing fellatio.",
+    "eyes": "Heart-shaped pupils, ahegao, or rolling back in pleasure.",
+    "arms": "Bracing on the surface (all fours), holding onto partners, or grabbing sheets.",
+    "hands": "Grabbing breasts, holding legs, fingering, or resting on knees/shoulders.",
+    "torso": "Nude, arching back, breasts exposed and pressed or being touched.",
+    "pelvis": "Engaged in intercourse, involving vaginal or anal penetration, potentially double penetration.",
+    "legs": "Spread wide, positioned in all fours, missionary, or reverse cowgirl depending on specific interaction.",
+    "feet": "Toes curled, dynamic positioning based on stance (kneeling or lying).",
+    "additional": "Sexual fluids, messy after-sex atmosphere, sweat, steaming body."
   },
   "lora": {
     "lora_name": "Illustrious/Poses/4P_sex.safetensors",
-    "lora_weight": 1.0,
-    "lora_triggers": "4P_sex"
+    "lora_weight": 0.6,
+    "lora_triggers": "4P_sexV1"
   },
   "tags": [
-    "4girls",
-    "group",
-    "tangled",
-    "multiple_viewers",
-    "all_fours",
-    "entangled_legs",
-    "close_contact",
-    "crowded"
+    "4P_sexV1",
+    "group sex",
+    "foursome",
+    "4P",
+    "double penetration",
+    "fellatio",
+    "all fours",
+    "uncensored",
+    "hetero",
+    "sex"
   ]
 }