Rename picture-targets to output-targets across entire codebase

Rename all Python modules, classes, API endpoints, config keys, frontend
fetch URLs, and Home Assistant integration URLs from picture-targets to
output-targets. Store loads both new and legacy JSON keys for backward
compatibility with existing data files.

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

server/src/wled_controller/storage/output_target.py

@@ -0,0 +1,62 @@
+"""Output target base data model."""
+
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Optional
+
+
+@dataclass
+class OutputTarget:
+    """Base class for output targets."""
+
+    id: str
+    name: str
+    target_type: str  # "wled", "key_colors", ...
+    created_at: datetime
+    updated_at: datetime
+    description: Optional[str] = None
+
+    def register_with_manager(self, manager) -> None:
+        """Register this target with the processor manager. Subclasses override."""
+        pass
+
+    def sync_with_manager(self, manager, *, settings_changed: bool, source_changed: bool, device_changed: bool) -> None:
+        """Push changed fields to a running processor. Subclasses override."""
+        pass
+
+    def update_fields(self, *, name=None, device_id=None, picture_source_id=None,
+                      settings=None, key_colors_settings=None, description=None,
+                      **_kwargs) -> None:
+        """Apply mutable field updates. Base handles common fields; subclasses handle type-specific ones."""
+        if name is not None:
+            self.name = name
+        if description is not None:
+            self.description = description
+
+    @property
+    def has_picture_source(self) -> bool:
+        """Whether this target type uses a picture source."""
+        return False
+
+    def to_dict(self) -> dict:
+        """Convert to dictionary."""
+        return {
+            "id": self.id,
+            "name": self.name,
+            "target_type": self.target_type,
+            "description": self.description,
+            "created_at": self.created_at.isoformat(),
+            "updated_at": self.updated_at.isoformat(),
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "OutputTarget":
+        """Create from dictionary, dispatching to the correct subclass."""
+        target_type = data.get("target_type", "led")
+        if target_type == "led":
+            from wled_controller.storage.wled_output_target import WledOutputTarget
+            return WledOutputTarget.from_dict(data)
+        if target_type == "key_colors":
+            from wled_controller.storage.key_colors_output_target import KeyColorsOutputTarget
+            return KeyColorsOutputTarget.from_dict(data)
+        raise ValueError(f"Unknown target type: {target_type}")