feat(lab-envs): TUI view for backend-agnostic ephemeral lab envs

[devin-ai-integration]

Summary

Adds a Lab Envs view to the Bubble Tea client mirroring the concave-web /lab/envs page and backed by the same backend-agnostic API introduced in concave#1.

Changes

• internal/client/client.go: LabEnv, LabStorage, LabEnvsResponse, LabLaunchRequest types and Client.LabEnvs / LabLaunch / LabExtend / LabArchive methods.
• cmd/concave-tui/model/api_bindings.go: apiLabEnvsFn / apiLabLaunchFn / apiLabExtendFn / apiLabArchiveFn — injectable function variables for tests.
• cmd/concave-tui/model/lab_envs.go: LabEnvsModel.
  • 10-second refresh tick for the env table.
  • 1-second tick for live TTL countdowns.
  • Keybindings: r refresh, j/k select, e extend +1h (developer+), a archive now (operator+).
  • Header shows active driver, hot tier, and cold tier so the operator sees where an archive will land.
  • Detail pane shows per-env Jupyter URL, hot/cold paths, and archive ref.
• cmd/concave-tui/model/root.go: new ViewLabEnvs slot in the view enum, wired into Update, activateView, deactivateView, activeContent, applyLayout, visibleViews, sidebarIcon, sidebarLabel, and the help overlay.
• Tests:
  • model/root_test.go: updated TestRootSwitchesViewsWhenAuthenticated (system is now the ninth key), TestAdminVisibleViewsIncludeSystemAndUsers (10 views), TestViewerVisibleViewsIncludeMonitoringScreens (7 views).
  • model/lab_envs_test.go: formatTTL rendering cases, LabEnvsModel table rendering + cold-tier header, and role-gated extend.

Gradient-specific touches

• Live TTL countdown with local tick (1s) + authoritative poll (10s) — matches the web countdown cadence without hammering the API.
• Role gating in lockstep with the server (auth.ActionStart extends, auth.ActionStop archives).
• Header surface the mesh-addressable cold tier path so an operator can reason about where an archive will be restorable from.

Review & Testing Checklist for Human

• Pair with concave#1 and concave-web#2 in a local Gradient box. Log into concave-tui, press 7 to jump to Lab Envs, and confirm the env list populates in parallel with the web page.
• Launch an env from the CLI (concave lab envs launch --image jupyter/minimal-notebook:latest --ttl 30m) and watch the TTL count down in the TUI without manual refresh.
• Press e as a developer and a as an operator. Confirm both actions succeed and the list refreshes.

Notes

• No new dependencies.
• The view shares no code with the existing phase 15 monitoring scaffolding on main; it's a standalone screen.

Link to Devin session: https://app.devin.ai/sessions/5d19efa113054ca4953d9ed9309ce705
Requested by: @ElFariss