Add dedicated graph transition screens

[forhappy]

Summary

• cover the full graph workspace while initial layouts settle or community details load
• keep the underlying canvas mounted but inert, and reveal the current layout after a 10-second escape hatch
• reuse the current Compass mark and restore the previous overview with an error banner when community loading fails

Verification

• viewer unit suite: 75 tests passed
• VS Code unit suite: 56 tests passed
• Playwright graph parity: 6 tests passed
• Playwright accessibility: 9 tests passed
• VSIX package and smoke check passed
• graphify update . completed