Version OpenCode skills and plugins

Repository sits at the OpenCode config root rather than inside skills/ or
plugins/. OpenCode scans exactly those two subdirectories, and a .git
directory inside either one is picked up as a plugin and fails to load:

  loading plugin id=.../plugins/.git entrypoint=.../plugins/.git/index
  failed to load plugin ... AggregateError: 2 errors building .../plugins/.git/index

The watcher.ignore config option does not help: it only suppresses filesystem
update events, not plugin discovery, and the "-" disable prefix only applies to
plugins listed in opencode.json(c), not auto-discovered ones.

.gitignore admits only skills/ and plugins/ (plus itself). Personal config
(opencode.jsonc, cli.json, service.json) and node_modules stay local.

skills/opencode-plugins  V2-only plugin authoring reference and 7 templates,
                         transcribed from the V2 docs with the URL on every file
plugins/searxng-search   searxng_search tool over a self-hosted SearXNG JSON API

skills/opencode-plugins/templates/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "opencode-acme-plugin",
+  "version": "1.0.0",
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts",
+    "./rpc": "./src/rpc.ts",
+    "./tui": "./src/tui.tsx"
+  },
+  "dependencies": {
+    "@opencode/plugin": "latest"
+  }
+}