fix(mobile): hide threads from switched-off environments

[entity]

Problem

On iOS, switching an environment off in Settings → Environments leaves its threads in the home list, the iPad sidebar, and the thread arrangement sheet. Because settle and snooze support only covers enabled environments, those threads also drop off the Settled and Snoozed shelves and show as active. Reported in #15098.

Change

navigationThreadShellsAtom in packages/client-runtime/src/state/threadShell.ts looped over every saved environment (catalog.entries.keys()). It now uses enabledEnvironmentIds(...), like threadRefsAtom, threadShellsAtom, the project atoms, and the server-config atoms beside it.

This puts mobile back to how it behaved before #2829 and matches web, which still uses the enabled-only useThreadShells(): threads from a switched-off environment leave the list and come back, with their settled state, when it's switched back on. The atom is only used by mobile (HomeRouteScreen, ThreadNavigationSidebar, ThreadArrangementSheet), so web is unaffected.

Scope and approval

Fixes #15098. The triage comment on that issue confirms the regression, traces it to this atom, and notes that web, and mobile before #2829, hide threads from switched-off environments. This PR restores that behavior. It doesn't take on the alternative of keeping the threads visible and still settled, which would need server configs or settled state kept for switched-off environments and is a separate product choice.

Verification

• Added leaves switched-off environments out of navigation to packages/client-runtime/src/state/threadShell.test.ts. With two environments, switching one off removes its threads from navigationThreadShellsAtom, and switching it back on brings them back.
• Without the fix, the new test fails (expected Set{ 'environment-v2', 'remote-environment-v2' } to deeply equal Set{ 'environment-v2' }). With the fix, all 5 tests in the file pass (vp test run packages/client-runtime/src/state/threadShell.test.ts).
• vp fmt --check and vp lint on both files and tsc --noEmit in packages/client-runtime pass.
• I haven't checked this in the iOS app, and there are no before/after screenshots from a device yet. The issue has before screenshots from the reporter.

[macroscopeapp]

Approvability

Verdict: Approved at f7913ce

Macroscope's review found this PR approvable — This is a narrowly scoped mobile bug fix that reuses the existing enabled-environment filter and adds a regression test for disabling and re-enabling environments. Existing enabled-environment behavior remains unchanged, with no schema, infrastructure, security, billing, or authentication impact.

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[entity]

Wow that was quick, thanks @juliusmarminge 🎉