feat(installer): add Hermes Agent target (#274)

Adds Hermes Agent (Nous Research) as a CodeGraph installer target. Writes mcp_servers.codegraph and ensures platform_toolsets.cli includes mcp-codegraph in $HERMES_HOME/config.yaml, with full installer contract-test coverage.

src/bin/codegraph.ts

@@ -1341,7 +1341,7 @@ program
  */
 program
   .command('install')
-  .description('Install codegraph MCP server into one or more agents (Claude Code, Cursor, Codex CLI, opencode)')
+  .description('Install codegraph MCP server into one or more agents (Claude Code, Cursor, Codex CLI, opencode, Hermes Agent)')
   .option('-t, --target <ids>', 'Target agent(s): comma-separated ids, or "auto"|"all"|"none". Default: prompt')
   .option('-l, --location <where>', 'Install location: "global" or "local". Default: prompt')
   .option('-y, --yes', 'Non-interactive: defaults to --location=global --target=auto, auto-allow on')