fix: harden mail thread navigation

[the-luap]

Summary

This PR hardens the mailbox thread/detail navigation flow and adds explicit controls for returning to the list.

It addresses the areas discussed in:

• Bug: mailbox route crashes after creating identity when default mailbox is not ready #425
• UX: message detail view needs obvious close and next/previous navigation #426
• Bug/UX: inconsistent message dates and missing thread conversation view #427

Changes

• Add a ThreadNavigationControls component with:
  • Close
  • Back to list
  • disabled Previous / Next placeholders for the adjacent-thread flow
  • keyboard shortcut: Esc to return to the list
• Preserve mailbox/list route state while opening thread detail pages.
• Avoid render-time thread side effects in the email renderer.
• Harden mailbox route handling when mailbox state is missing or still loading.

Follow-up

The adjacent-thread previous/next timestamp query has been removed from this PR after review feedback. That date/time ordering logic can be handled separately in a smaller follow-up PR.

Screenshot

Sensitive mailbox/account names, sender/recipient data, subject, and message content are redacted.

Verification

• git diff --check upstream/main...HEAD passes.
• pnpm install --frozen-lockfile passes.
• pnpm --filter @kurrier/web exec tsc --noEmit --pretty false currently reports pre-existing upstream errors unrelated to this diff:
  • ComposeMail callers missing identityMailboxes in files unchanged by this PR.
  • components/ui/sonner.tsx CSSProperties type mismatch in a file unchanged by this PR.
• pnpm --filter @kurrier/web lint currently reports existing Biome formatting/style diagnostics across the app, including files not touched by this PR.

[the-luap]

Added a redacted real screenshot showing the new Close / Back to list / Previous / Next thread navigation controls. Sensitive mailbox/account names, sender/recipient data, subject, and message content are redacted.\n\n

[krokhale]

This looks great, but when i view a thread on your branch, I am getting a SQL error on this branch: the-luap/paul/thread-navigation-safe-routes

You are probably passing one field as a DB timestamp/string and another as a JS Date/string.

Or we could skip the date/time stuff for now (something in future or another PR) while the rest looks good.

[the-luap]

Thanks for checking it. I removed the adjacent-thread timestamp query from this PR in commit 9814d92, so the date/time ordering issue is out of scope here now.\n\nThe PR keeps the explicit Close / Back to list controls and leaves Previous / Next as disabled placeholders. We can handle adjacent-thread ordering in a smaller follow-up PR once the timestamp typing is nailed down.