Show file paths above open pages

[shobhit-seg]

Summary

• show a navigable folder path above every open native or linked page
• resolve authorized ancestors server-side with missing-parent, cycle, and depth safeguards
• collapse deep paths into an accessible menu and refresh trails after hierarchy changes

Validation

• shared, API, and web typechecks passed on Node 24.18.0
• 52 tests passed: shared 22, API 10, web 20
• focused Biome checks and staged diff checks passed
• production web build passed
• desktop and narrow responsive browser verification passed