chore: migrate MCP config from .vscode/mcp.json to .mcp.json (#822)

Per https://gh.io/copilotcli-mcpmigrate, Copilot CLI loads workspace MCP servers from .mcp.json at the repo root (not .vscode/mcp.json). Rename the file and switch the top-level key from `servers` to `mcpServers` so the github-agentic-workflows server is discovered by `copilot mcp list`.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jamesadevine

.vscode/mcp.json .mcp.json.vscode/mcp.json renamed to .mcp.json

@@ -1,5 +1,5 @@
 {
-  "servers": {
+  "mcpServers": {
     "github-agentic-workflows": {
       "command": "gh",
       "args": [
@@ -8,4 +8,4 @@
       ]
     }
   }
-}
+}