Configurable RSpec focus tag

Resolves #1.

Summary

Makes the RSpec focus tag configurable so you can use :focus, :wip, or any other symbol. The tag is configurable in Settings (UI) and in settings.json.

Changes

• Configuration
  • New setting rspec-focus.focusTag (default: "focus").
  • Available under Settings → RSpec Focus and in JSON as "rspec-focus.focusTag": "wip" (or another value).
• Extension
  • Add and Clear commands use the configured tag (e.g. , :focus or , :wip).
  • Tag value is sanitized: leading colons are stripped and only [a-zA-Z0-9_] are allowed; invalid/empty values fall back to "focus".
• Tests
  • Tests updated for the new behavior and to cover the configurable tag (e.g. wip).
• Refactor
  • Main entry renamed from rspec-focus.ts to extension.ts and test file to extension.test.ts to match common VS Code extension layout.

Usage

• Settings UI: Search for “RSpec Focus” or “focus tag” and set Focus Tag (e.g. wip).
• settings.json:
  "rspec-focus.focusTag": "wip"

With "wip", RSpec Focus: Add inserts , :wip and RSpec Focus: Clear removes , :wip only. Default remains "focus" so existing behavior is unchanged.