fix(spore): fix Log Explorer host variable query (#391)

label_values({}, host) fails because Loki requires at least one
matcher in stream selectors. Use label_values(host) instead, set
default selection to All, and bind the variable to the Loki
datasource explicitly.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: stackptr

hosts/spore/services/dashboards/logs.json

@@ -180,17 +180,19 @@
   "templating": {
     "list": [
       {
-        "current": {},
+        "current": { "selected": true, "text": "All", "value": "$__all" },
         "hide": 0,
         "includeAll": true,
+        "allValue": ".*",
         "label": "Host",
         "multi": true,
         "name": "host",
         "options": [],
-        "query": "label_values({}, host)",
+        "query": "label_values(host)",
         "refresh": 2,
         "regex": "",
-        "type": "query"
+        "type": "query",
+        "datasource": { "type": "loki", "uid": "${datasource}" }
       },
       {
         "current": { "selected": false, "text": "", "value": "" },