feat: add StabilityMatrix-style Model Manager service

New FastAPI container (port 8189) to download and manage models:
- Installed Models, Add/Download (CivitAI/HuggingFace/direct URL), Settings views
- Persistent SQLite storage for API keys and download history (./sparkyui-data)
- Downloads land in ./models, auto-sorted into ComfyUI's standard subfolders
- Default COMFYUI_HOST_PATH and SPARKYUI_DATA_PATH to the project root
- Wire docker-compose service, env defaults, gitignore, README docs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

model-manager/app/config.py

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+"""Paths, model-type mapping, and folder bootstrap for the Model Manager."""
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+# Root of the host `models/` directory (mounted read-write into this container).
+MODELS_DIR = Path(os.environ.get("MODELS_DIR", "/models")).resolve()
+
+# Persistent data dir for the SQLite database.
+DATA_DIR = Path(os.environ.get("DATA_DIR", "/data")).resolve()
+
+DB_PATH = DATA_DIR / "manager.db"
+
+# StabilityMatrix-style model types mapped to ComfyUI's standard `models/` subfolders.
+# `key` is the stable id used by the API/UI; `folder` is the on-disk subdirectory.
+MODEL_TYPES: list[dict[str, str]] = [
+    {"key": "checkpoint", "label": "Checkpoint", "folder": "checkpoints"},
+    {"key": "lora", "label": "LoRA / LyCORIS", "folder": "loras"},
+    {"key": "vae", "label": "VAE", "folder": "vae"},
+    {"key": "embedding", "label": "Textual Inversion", "folder": "embeddings"},
+    {"key": "controlnet", "label": "ControlNet", "folder": "controlnet"},
+    {"key": "upscaler", "label": "Upscaler", "folder": "upscale_models"},
+    {"key": "clip", "label": "CLIP", "folder": "clip"},
+    {"key": "clip_vision", "label": "CLIP Vision", "folder": "clip_vision"},
+    {"key": "text_encoder", "label": "Text Encoder", "folder": "text_encoders"},
+    {"key": "diffusion_model", "label": "Diffusion Model (UNET)", "folder": "diffusion_models"},
+    {"key": "unet", "label": "UNET", "folder": "unet"},
+    {"key": "hypernetwork", "label": "Hypernetwork", "folder": "hypernetworks"},
+    {"key": "style_model", "label": "Style Model", "folder": "style_models"},
+    {"key": "gligen", "label": "GLIGEN", "folder": "gligen"},
+    {"key": "vae_approx", "label": "VAE Approx", "folder": "vae_approx"},
+    {"key": "ipadapter", "label": "IP-Adapter", "folder": "ipadapter"},
+    {"key": "other", "label": "Other", "folder": "other"},
+]
+
+# Quick lookups.
+TYPE_BY_KEY: dict[str, dict[str, str]] = {t["key"]: t for t in MODEL_TYPES}
+FOLDER_BY_KEY: dict[str, str] = {t["key"]: t["folder"] for t in MODEL_TYPES}
+KEY_BY_FOLDER: dict[str, str] = {t["folder"]: t["key"] for t in MODEL_TYPES}
+
+
+def folder_for_type(type_key: str) -> str:
+    """Return the on-disk subfolder for a model type key, defaulting to `other`."""
+    return FOLDER_BY_KEY.get(type_key, "other")
+
+
+def ensure_dirs() -> None:
+    """Create the data dir and all standard model subfolders if missing."""
+    DATA_DIR.mkdir(parents=True, exist_ok=True)
+    MODELS_DIR.mkdir(parents=True, exist_ok=True)
+    for t in MODEL_TYPES:
+        (MODELS_DIR / t["folder"]).mkdir(parents=True, exist_ok=True)