Replace auto-start with startup automation, add card colors to dashboard

- Add `startup` automation condition type that activates on server boot,
  replacing the per-target `auto_start` flag
- Remove `auto_start` field from targets, scene snapshots, and all API layers
- Remove auto-start UI section and star buttons from dashboard and target cards
- Remove `color` field from scene presets (backend, API, modal, frontend)
- Add card color support to scene preset cards (color picker + border style)
- Show localStorage-backed card colors on all dashboard cards (targets,
  automations, sync clocks, scene presets)
- Fix card color picker updating wrong card when duplicate data attributes
  exist by using closest() from picker wrapper instead of global querySelector
- Add sync clocks step to Sources tab tutorial
- Bump SW cache v9 → v10

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

server/src/wled_controller/storage/automation.py

@@ -32,6 +32,8 @@ class Condition:
             return MQTTCondition.from_dict(data)
         if ct == "webhook":
             return WebhookCondition.from_dict(data)
+        if ct == "startup":
+            return StartupCondition.from_dict(data)
         raise ValueError(f"Unknown condition type: {ct}")
 
 
@@ -177,6 +179,17 @@ class WebhookCondition(Condition):
         return cls(token=data.get("token", ""))
 
 
+@dataclass
+class StartupCondition(Condition):
+    """Activate when the server starts — stays active while enabled."""
+
+    condition_type: str = "startup"
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "StartupCondition":
+        return cls()
+
+
 @dataclass
 class Automation:
     """Automation that activates a scene preset based on conditions."""