prep to release 1.6.0

[devoncarew]

• prep to release 1.6.0

[github-actions]

Note: merging this PR will create a new release.

1.6.0

• Added support for Cursor (note: not yet in cursor.com/marketplace /
  cursor.directory).
• Replaced the per-agent package validation hooks with a single add-package
  skill. The skill fires when an agent is about to add a Dart or Flutter package
  and instructs it to read flutter pub add output for discontinued-package and
  outdated-version warnings. Equivalent guidance is embedded in the Gemini CLI
  context file. This eliminates the per-agent hook infrastructure (different
  event names, field shapes, and invocation styles across Claude Code, Gemini
  CLI, and GitHub Copilot) and the external pub.dev network calls at hook time.
• Added a slipstream-packages skill that instructs the agent to use the
  packages MCP tools when writing code against an unfamiliar pub package or one
  whose version may be newer than its training data.
• Renamed the 'flutter-slipstream' skill to 'slipstream-inspector'.
• Updated the privacy policy to note that we no longer make calls to
  https://pub.dev for package metadata.
• Removed the Bash MCP entrypoint scripts in favor of calling the Dart MCP
  entrypoints directly.