✨ Issue Navigator

### Description

Introduce an Issue Navigator in CodeEdit that displays a list of build, runtime, or linter issues in a centralized and navigable interface. This navigator should help users quickly identify and jump to problems in their project, improving debugging efficiency and overall workflow.

The navigator should display errors, warnings, and informational messages in a hierarchical or grouped manner, potentially organized by file or type. It should also stay synchronized with diagnostics displayed in the source editor via Line Annotations.

### Requirements

- A dedicated navigator labeled “Issues”
- Group issues by file
- Show concise descriptions with icons to indicate severity
- Allow clicking on an issue to navigate to the corresponding line in the source file
- Real-time updates as issues are added, removed, or resolved
- Optional filters to show/hide specific severity levels
- Support for issues emitted by:
- Build systems
- Linters
- Runtime logs (if applicable in future development)
- Issues in the Issue Navigator should match in the editor (text, type, and icons used)

### Additional Context

The Issue Navigator will complement other navigators like Project and Source Control by providing a dedicated space for surfacing problems in the codebase. It should feel native to the rest of CodeEdit’s UI, aligning with existing navigation and pane behaviors.

We should use the `DiagnosticManager` in #2014 so that issues remain in sync with issues in the source editor (#2015).

### Related Issues

- #2014
- #2015
- https://github.com/CodeEditApp/CodeEditSourceEditor/issues/297