feat(installer): GitHub Copilot targets — VS Code, Copilot CLI, JetBrains

Adds three new installer targets so `codegraph install` can wire the
MCP server into GitHub Copilot surfaces:

- copilot-vscode: .vscode/mcp.json (local) or the VS Code User-dir
  mcp.json (global), JSONC-surgical edits, `--path` pinned via
  ${workspaceFolder} for global installs
- copilot-cli: ~/.copilot/mcp-config.json
- copilot-jetbrains: github-copilot config dir (XDG / %LOCALAPPDATA%)

Detection, install, uninstall, and --print-config are covered for all
three in installer-targets.test.ts, including platform-specific path
resolution.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/bin/codegraph.ts

@@ -2232,7 +2232,7 @@ program
  */
 program
   .command('install')
-  .description('Install codegraph MCP server into one or more agents (Claude Code, Cursor, Codex CLI, opencode, Hermes Agent)')
+  .description('Install codegraph MCP server into one or more agents (Claude Code, Cursor, Codex CLI, opencode, Hermes Agent, Gemini CLI, Antigravity IDE, Kiro, GitHub Copilot)')
   .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')
@@ -2332,7 +2332,7 @@ program
  */
 program
   .command('uninstall')
-  .description('Remove codegraph from your agents (Claude Code, Cursor, Codex CLI, opencode, Hermes Agent)')
+  .description('Remove codegraph from your agents (Claude Code, Cursor, Codex CLI, opencode, Hermes Agent, Gemini CLI, Antigravity IDE, Kiro, GitHub Copilot)')
   .option('-t, --target <ids>', 'Target agent(s): comma-separated ids, or "all". Default: all')
   .option('-l, --location <where>', 'Uninstall location: "global" or "local". Default: prompt')
   .option('-y, --yes', 'Non-interactive: defaults to --location=global --target=all')