Add router-backed app navigation and skeleton loading states

[wesbillman]

Summary

• add TanStack Router with hash-history app navigation for home, agents, workflows, channels, forum threads, and search-result deep links
• move shell navigation state out of scattered local state and into typed route params/search state
• replace the generic Loading ... screens with route- and screen-shaped skeleton states for agents, workflows, channels, and forum loads
• add a local jdenticon type declaration needed after rebasing onto current main

Testing

• source ../bin/activate-hermit && pnpm check
• source ../bin/activate-hermit && pnpm build
• source ../bin/activate-hermit && pnpm exec playwright test tests/e2e/navigation.spec.ts tests/e2e/workflows.spec.ts tests/e2e/smoke.spec.ts tests/e2e/channel-browser.spec.ts
• git push -u origin tanstack-router-navigation pre-push hook
  • desktop check/build
  • desktop tauri check
  • rust fmt/clippy
  • rust unit tests