[0.1.5] Add Doctor diagnostics action

[unurgunite]

Description

Adds a DocScribe Doctor action that diagnoses the plugin setup and reports a comprehensive summary.

When invoked (Editor Popup -> DocScribe -> DocScribe Doctor), it collects and displays:

• Project root and Gemfile location
• Ruby SDK configured in the IDE (name, home path) and resolved Ruby binary
• docscribe gem status (AVAILABLE / MISSING / UNCHECKED), version, and server mode support
• Daemon server running state and fallback explanation
• Current plugin settings (hideCommentsByDefault)
• Issues summary with actionable steps when something is misconfigured

Implementation

• DoctorAction.kt — new AnAction available for any open project (no file requirement). Builds a multi-line diagnostic report and displays it via the DocScribe notification group.
• DocscribeDaemon.kt — added 4 public accessors (getRubyPath(), getDocscribeStatus(), getCapabilities(), isServerRunning()) that expose previously internal/private state in a controlled way.
• plugin.xml — registered action and added to the DocScribe group with a separator.

Testing

• DoctorActionTest.kt — 3 tests covering enabled state with project, disabled without project, and BGT update thread.
• All existing tests pass (119 total).

Checklist

• Tests pass (./gradlew test)
• Formatting clean (./gradlew spotlessCheck)
• Static analysis clean (./gradlew detekt)
• Plugin verified (./gradlew verifyPlugin)
• CHANGELOG updated