feat(diagnostics): add scrollable problems popover and click-to-jump navigation

[Yan123-tech]

Summary

This PR addresses the user requirement for interactive diagnostic inspection and editor jump navigation:

• Converts the status bar error/warning indicator in the bottom-right corner into an interactive clickable button.
• Adds DiagnosticsListView, a scrollable popover displaying all diagnostic errors, warnings, line/column coordinates (Ln X, Col Y), error messages, and LSP sources (e.g., gopls, sourcekit-lsp).
• Implements click-to-jump navigation: clicking any problem item closes the popover, scrolls the editor to center the error line, selects the exact range, and flashes a focus emphasis highlight.
• Makes DocumentDiagnostic conform to Identifiable with a deterministic identifier.
• Adds comprehensive unit tests for diagnostic sorting and identification.

Key Changes

1. Interactive Status Bar Counter:
   • In StatusBarView.swift, transformed static count text into an interactive button with hover states.
   • Popover is anchored to the bottom-right diagnostic counter and opens upwards.
2. Scrollable Diagnostics Popover (DiagnosticsListView.swift):
   • Displays problems header with filename and total error/warning count pills.
   • Scrollable problem list with severity icons (red circle for errors, yellow triangle for warnings).
   • Clean hover feedback and empty state.
3. Click-to-Jump & Flash Highlight:
   • In AppState.swift, added diagnosticJumpRequest and jumpTo(diagnostic:in:).
   • In CodeEditorView.swift, handles jump requests by delegating to LSPTextViewCoordinator.
   • In LSPTextViewCoordinator.swift, jumpTo(range:) sets the selection, centers the viewport via scrollToRange(range, center: true), makes the text view first responder, and flashes an Emphasis highlight.
4. Testing:
   • All 125 unit tests passing.
   • Verified with strict swift-format lint and scripts/build-app.sh application bundle build.

Testing & Verification

• swift test passes (125 tests across 34 suites)
• xcrun swift-format lint --strict clean (0 warnings)
• scripts/build-app.sh completes successfully with valid code signature