fix(playwright-pro): make TestRail/BrowserStack MCP servers opt-in instead of always-failing (#978)

The two MCP servers registered in .mcp.json could never start: their
@modelcontextprotocol/sdk dependency is declared but never installed
(the plugin ships no node_modules and nothing runs npm install), so every
user saw a permanent 'Failed to connect' pair in `claude mcp list`.

Per the reporter's option 4 + docs: the registrations move to
integrations/mcp-servers.example.json (no longer auto-loaded), and the
README's Integrations Setup section now documents the two-step opt-in
(npm install inside the integration folder, copy the example to .mcp.json).
The integrations themselves are unchanged and keep working for users who
enable them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qgc6RYXWJPr5oW9DHU7zR4

engineering-team/playwright-pro/README.md

@@ -80,6 +80,23 @@ Ready-to-use, parametrizable templates covering:
 
 ## Integrations Setup
 
+The TestRail and BrowserStack MCP servers are **opt-in** (issue #978): they need
+`npm install` inside their integration folders, which the plugin install never
+runs — so they are no longer registered by default (previously they showed as a
+permanent `Failed to connect` pair in `claude mcp list` for every user).
+
+To enable one (or both):
+
+```bash
+# 1. Install the server dependencies inside the installed plugin
+cd "$(claude plugin path playwright-pro)"/integrations/testrail-mcp && npm install
+cd ../browserstack-mcp && npm install   # if you also want BrowserStack
+
+# 2. Activate the server registrations
+cp ../mcp-servers.example.json ../../.mcp.json
+# (delete the server block you don't use from the copied file)
+```
+
 ### TestRail (Optional)
 
 Set environment variables: