Add project-aware code navigation to diff review

[imjyz]

Diffs alone often lack enough context for reviewing changes in large projects.

It would be helpful if Kanban supported IDE-like project navigation during diff review:

• Browse the full project source from the diff
• Jump to symbol definitions and implementations
• Find usages and related code
• Keep the diff and source context linked

IntelliJ IDEA's diff works well for this because the project is indexed and changed code remains navigable. Similar capabilities, either built in or through IDE/LSP integration, would make Kanban's review workflow much more effective, especially for Java projects.