feat(frontend): improve architecture graph readability

[SHAURYAKSHARMA24]

Closes #112

Summary

• Arrange architecture nodes left-to-right by detected layer.
• Display node type, layer, and relationship state.
• Add collapsible architecture layers.
• Improve node sizing, spacing, and graph fit behavior.
• Add focused tests for layout and node metadata.

Validation

• Focused Vitest: 4 tests passed across 2 files.
• Targeted ESLint: passed.
• git diff --check: passed.