fix(plugin): inline mcpServers in plugin.json so the MCP server actually loads

/reload-plugins reported '0 plugin MCP servers'. Root cause: plugin.json had
"mcpServers": "./.mcp.json" — a string path, which is neither a valid inline
object nor a recognized reference (per docs, plugin MCP servers are a root
.mcp.json OR an inline object in plugin.json), so it parsed to zero servers.

Inline the mcpServers object directly in plugin.json and remove the separate
.mcp.json. The user_config substitution syntax was already correct
(plugins-reference: values substitute as ${user_config.KEY} in MCP configs).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugin/.claude-plugin/plugin.json

@@ -3,7 +3,13 @@
   "description": "Scribe second brain for Claude Code: MCP tools over your notes/tasks/projects/rules, a session-start push channel that surfaces your always-on rules + active-project context, and a set of universal process-skills (brainstorm, debug, TDD, plan, verify). Replaces superpowers + file-memory with one app-backed plugin.",
   "version": "0.1.0",
   "author": { "name": "Bryan Van Deusen" },
-  "mcpServers": "./.mcp.json",
+  "mcpServers": {
+    "scribe": {
+      "type": "http",
+      "url": "${user_config.api_endpoint}/mcp",
+      "headers": { "Authorization": "Bearer ${user_config.api_token}" }
+    }
+  },
   "userConfig": {
     "api_endpoint": {
       "type": "string",