feat: migrate storage from JSON files to SQLite

Replace 22 individual JSON store files with a single SQLite database
(data/ledgrab.db). All entity stores now use BaseSqliteStore backed by
SQLite with WAL mode, write-through caching, and thread-safe access.

- Add Database class with SQLite backup/restore API
- Add BaseSqliteStore as drop-in replacement for BaseJsonStore
- Convert all 16 entity stores to SQLite
- Move global settings (MQTT, external URL, auto-backup) to SQLite
  settings table
- Replace JSON backup/restore with SQLite snapshot backups (.db files)
- Remove partial export/import feature (backend + frontend)
- Update demo seed to write directly to SQLite
- Add "Backup Now" button to settings UI
- Remove StorageConfig file path fields (single database_file remains)

server/src/wled_controller/api/routes/system_settings.py

@@ -4,15 +4,14 @@ Extracted from system.py to keep files under 800 lines.
 """
 
 import asyncio
-import json
 import logging
 import re
-from pathlib import Path
 
-from fastapi import APIRouter, HTTPException, Query, WebSocket, WebSocketDisconnect
+from fastapi import APIRouter, Depends, HTTPException, Query, WebSocket, WebSocketDisconnect
 from pydantic import BaseModel
 
 from wled_controller.api.auth import AuthRequired
+from wled_controller.api.dependencies import get_database
 from wled_controller.api.schemas.system import (
     ExternalUrlRequest,
     ExternalUrlResponse,
@@ -22,6 +21,7 @@ from wled_controller.api.schemas.system import (
     MQTTSettingsResponse,
 )
 from wled_controller.config import get_config
+from wled_controller.storage.database import Database
 from wled_controller.utils import get_logger
 
 logger = get_logger(__name__)
@@ -33,21 +33,9 @@ router = APIRouter()
 # MQTT settings
 # ---------------------------------------------------------------------------
 
-_MQTT_SETTINGS_FILE: Path | None = None
 
-
-def _get_mqtt_settings_path() -> Path:
-    global _MQTT_SETTINGS_FILE
-    if _MQTT_SETTINGS_FILE is None:
-        cfg = get_config()
-        # Derive the data directory from any known storage file path
-        data_dir = Path(cfg.storage.devices_file).parent
-        _MQTT_SETTINGS_FILE = data_dir / "mqtt_settings.json"
-    return _MQTT_SETTINGS_FILE
-
-
-def _load_mqtt_settings() -> dict:
-    """Load MQTT settings: YAML config defaults overridden by JSON overrides file."""
+def _load_mqtt_settings(db: Database) -> dict:
+    """Load MQTT settings: YAML config defaults overridden by DB settings."""
     cfg = get_config()
     defaults = {
         "enabled": cfg.mqtt.enabled,
@@ -58,31 +46,20 @@ def _load_mqtt_settings() -> dict:
         "client_id": cfg.mqtt.client_id,
         "base_topic": cfg.mqtt.base_topic,
     }
-    path = _get_mqtt_settings_path()
-    if path.exists():
-        try:
-            with open(path, "r", encoding="utf-8") as f:
-                overrides = json.load(f)
-            defaults.update(overrides)
-        except Exception as e:
-            logger.warning(f"Failed to load MQTT settings override file: {e}")
+    overrides = db.get_setting("mqtt")
+    if overrides:
+        defaults.update(overrides)
     return defaults
 
 
-def _save_mqtt_settings(settings: dict) -> None:
-    """Persist MQTT settings to the JSON override file."""
-    from wled_controller.utils import atomic_write_json
-    atomic_write_json(_get_mqtt_settings_path(), settings)
-
-
 @router.get(
     "/api/v1/system/mqtt/settings",
     response_model=MQTTSettingsResponse,
     tags=["System"],
 )
-async def get_mqtt_settings(_: AuthRequired):
+async def get_mqtt_settings(_: AuthRequired, db: Database = Depends(get_database)):
     """Get current MQTT broker settings. Password is masked."""
-    s = _load_mqtt_settings()
+    s = _load_mqtt_settings(db)
     return MQTTSettingsResponse(
         enabled=s["enabled"],
         broker_host=s["broker_host"],
@@ -99,9 +76,9 @@ async def get_mqtt_settings(_: AuthRequired):
     response_model=MQTTSettingsResponse,
     tags=["System"],
 )
-async def update_mqtt_settings(_: AuthRequired, body: MQTTSettingsRequest):
+async def update_mqtt_settings(_: AuthRequired, body: MQTTSettingsRequest, db: Database = Depends(get_database)):
     """Update MQTT broker settings. If password is empty string, the existing password is preserved."""
-    current = _load_mqtt_settings()
+    current = _load_mqtt_settings(db)
 
     # If caller sends an empty password, keep the existing one
     password = body.password if body.password else current.get("password", "")
@@ -115,7 +92,7 @@ async def update_mqtt_settings(_: AuthRequired, body: MQTTSettingsRequest):
         "client_id": body.client_id,
         "base_topic": body.base_topic,
     }
-    _save_mqtt_settings(new_settings)
+    db.set_setting("mqtt", new_settings)
     logger.info("MQTT settings updated")
 
     return MQTTSettingsResponse(
@@ -133,44 +110,25 @@ async def update_mqtt_settings(_: AuthRequired, body: MQTTSettingsRequest):
 # External URL setting
 # ---------------------------------------------------------------------------
 
-_EXTERNAL_URL_FILE: Path | None = None
-
-
-def _get_external_url_path() -> Path:
-    global _EXTERNAL_URL_FILE
-    if _EXTERNAL_URL_FILE is None:
-        cfg = get_config()
-        data_dir = Path(cfg.storage.devices_file).parent
-        _EXTERNAL_URL_FILE = data_dir / "external_url.json"
-    return _EXTERNAL_URL_FILE
-
-
-def load_external_url() -> str:
+def load_external_url(db: Database | None = None) -> str:
     """Load the external URL setting. Returns empty string if not set."""
-    path = _get_external_url_path()
-    if path.exists():
-        try:
-            with open(path, "r", encoding="utf-8") as f:
-                data = json.load(f)
-            return data.get("external_url", "")
-        except Exception:
-            pass
+    if db is None:
+        from wled_controller.api.dependencies import get_database
+        db = get_database()
+    data = db.get_setting("external_url")
+    if data:
+        return data.get("external_url", "")
     return ""
 
 
-def _save_external_url(url: str) -> None:
-    from wled_controller.utils import atomic_write_json
-    atomic_write_json(_get_external_url_path(), {"external_url": url})
-
-
 @router.get(
     "/api/v1/system/external-url",
     response_model=ExternalUrlResponse,
     tags=["System"],
 )
-async def get_external_url(_: AuthRequired):
+async def get_external_url(_: AuthRequired, db: Database = Depends(get_database)):
     """Get the configured external base URL."""
-    return ExternalUrlResponse(external_url=load_external_url())
+    return ExternalUrlResponse(external_url=load_external_url(db))
 
 
 @router.put(
@@ -178,10 +136,10 @@ async def get_external_url(_: AuthRequired):
     response_model=ExternalUrlResponse,
     tags=["System"],
 )
-async def update_external_url(_: AuthRequired, body: ExternalUrlRequest):
+async def update_external_url(_: AuthRequired, body: ExternalUrlRequest, db: Database = Depends(get_database)):
     """Set the external base URL used in webhook URLs and other user-visible URLs."""
     url = body.external_url.strip().rstrip("/")
-    _save_external_url(url)
+    db.set_setting("external_url", {"external_url": url})
     logger.info("External URL updated: %s", url or "(cleared)")
     return ExternalUrlResponse(external_url=url)