feat: add plugin store index

- Add store.json for plugin listing
- Auto-generate store.json in CI workflow

scripts/generate-store.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+set -e
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+STORE_FILE="$REPO_ROOT/store.json"
+
+echo "["
+
+first=true
+for manifest in "$REPO_ROOT"/plugins/*/manifest.json; do
+    [ -f "$manifest" ] || continue
+
+    if [ "$first" = true ]; then
+        first=false
+    else
+        echo ","
+    fi
+
+    cat "$manifest"
+done
+
+echo "]"