Migrate to type-safe navigation routes and harden the org link flow

[cynthiabondi]

Related PRs: #1196 #1197

Summary
Upgrade Compose Navigation to use type-safe routes, and fix several critical safety issues discovered during an audit of the org link flow.

Motivation
String-based routes are fragile and error-prone. The org link flow audit revealed data loss risks, crash vectors on malformed deep links, force-unwrap crashes, main-thread blocking, and scope lifecycle bugs.

Acceptance criteria

• Migrate all navigation to typed routes (replacing string literals)
• Fix tree save data loss — await save before navigating
• Wrap deep link JSON parsing in try/catch with fallback to default org
• Replace all force-unwrap (!!) with safe access and fallback behaviour
• Replace runBlocking on main thread with suspend functions
• Add re-entrance guards for Koin scope lifecycle
• Add RouteRegistry with route validation and stable alias support
• Add bounds checking in navFromNewUserCreation()
• Replace stringly-typed feature flags with OrgFeature enum

References
Closes #1196, #1197

[cynthiabondi]

Completed in #1196 and #1197