Replace Readme with interactive Guide panel and improve Context tab behavior

[Idddd]

Motivation

• Replace the static Readme with an interactive Guide that helps users discover and configure features and setup the plugin.
• Improve UX by auto-selecting the Context tab when new history arrives and provide quick links to settings and other tabs.
• Surface setup progress (LLM and prompt repo) and provide contextual actions to guide users to configuration pages.

Description

• Renamed the "Readme" tab to "Guide" and replaced createReadmePanel(bgColor, fgColor, borderColor, commonFont) with createReadmePanel(project, bgColor, fgColor, borderColor, commonFont) to build a new interactive guide UI.
• Implemented a rich guide layout with feature cards, details panel, welcome/setup banner, progress indicators, and action buttons that open settings or switch tabs; introduced GuideFeature data class, helper UI functions, and theme-aware colors.
• Restored and enhanced the ContextBoxStateService message bus subscription to render snapshots and automatically select the "Context" tab when snapshot history is present.
• Added imports for ShowSettingsUtil and Cursor, and integrated LlmSettingsLoader checks to compute setup state and conditionally render setup prompts.

Testing

• Ran a project build for the plugin module with ./gradlew :plugin-idea:build which completed successfully.
• Verified that the new Guide panel renders and that selecting feature cards updates the details pane via local UI smoke checks (no automated UI tests were included).

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Codex Task