Add AI Context Box tool window, Prompt Manager UI, and branch-diff integration with generation diffs

[Idddd]

Motivation

• Provide a persistent, visible AI "Context Box" for showing generation results and branch analysis summaries in the IDE.
• Improve prompt editing UX by consolidating prompt controls into a Prompt Manager UI used in both settings and the tool window.
• Capture and surface generated test file diffs and branch summaries so users can inspect AI outputs and analysis in one place.
• Make small project/build and icon updates to support the new UI and actions.

Description

• Added a project service ContextBoxStateService that stores the latest AI snapshot and publishes updates via a message bus Topic and ContextBoxListener.
• Implemented ContextBoxToolWindowFactory to host a read-only "Results" view and a Prompt Manager tab; prompts can be edited, saved, and reloaded via LlmSettingsLoader and Notifications.
• Refactored settings UI to use a shared Prompt Manager builder (buildPromptManagerPanel) and added SwingUtilities usage for UI updates.
• Updated GenerateTestsService to capture previous file content, compute a simple unified diff via buildCodeDiff, and push a generation snapshot to ContextBoxStateService after file creation; notifications are still sent for generated files.
• Enhanced SummarizeBranchDiffAction to resolve the current repository branch, derive a target branch/commit from VCS Log selection, call AiBranchDiffSummaryService, and publish branch analysis into the Context Box; added new action variants and registered them in plugin.xml.
• Replaced the previous icon and added blue-bulb.svg to resources; updated OpenProjectXIcons and several action icon paths.
• Adjusted plugin-idea/build.gradle.kts to provide defaults for platformType and platformVersion properties and switched the intellijPlatform dependency creation call accordingly.
• Updated plugin.xml to register the new tool window and new VCS log/context menu action entries.

Testing

• Built the project and plugin module using Gradle via ./gradlew build and ./gradlew :plugin-idea:assemble, and the build completed successfully.
• Verified the plugin wiring by running the IDE plugin run configuration (manual smoke run used for UI verification) which loaded the new tool window and actions without runtime errors.

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Codex Task