feat: dedicated server StatusPage for lifecycle states

[harshithmohan]

Summary

Adds a dedicated, full-bleed StatusPage (/webui/status) that is the single canonical surface for all non-ready server states — Starting, Failed, Restarting, Shutting-down, Shutdown, and Offline — plus an automatic recovery redirect back into the app once the server is Started. This fixes the auto-login gap that occurred when the server transitioned Starting → Started while the user was on the login page.

Why

• LoginPage lived outside AuthenticatedRoute, so the Starting state was handled ad-hoc there and the Starting → Started transition was never reliably caught (auto-login gap during the boot window).
• A 502 during Starting produced a blank crossfade / stuck state because nothing canonical owned the "server not reachable yet" state.
• Auto-login could fire during the boot window, racing server readiness.
• Restart/shutdown had no canonical UX; SignalR toasts and route guards fought the in-progress action.

Changes

• New serverLifecycle slice (src/core/slices/serverLifecycle.ts) — ephemeral UI intent (idle | restarting | shutting-down, initiatedAt). Deliberately excluded from sessionStorage persistence (both loadState and saveState in src/core/localStorage.ts) so a reload mid-restart never rehydrates a stale restarting and traps the user on a stuck StatusPage.
• New StatusPage.tsx (src/pages/StatusPage.tsx) — 7 variants (loading, starting, failed, restarting, shutting-down, shutdown, offline). Drive text via variantDetailMap and icons via variantIconMap. Polling at 2s / retry 5s that backs off to 15s / 15s once the server is unreachable. A 3-minute restart timeout promotes restarting → offline; 2 consecutive failures promotes shutting-down → shutdown. Immediate redirect on Started is guarded by lastSeenStartedAtRef + sawDisruptionRef + STATUS_FRESH_MS so the redirect only fires after a genuine disruption. Variants failed/offline/shutdown render action buttons — "Restart Server" (gated on CanRestart), "Retry Now", and "Retry Connection" respectively — so recovery is possible directly from the page.
• AuthenticatedRoute guard (src/core/router/AuthenticatedRoute.tsx) — isError or active lifecycle action → StatusPage; Waiting → login; Started → authenticated children / login redirected; Starting/Failed → StatusPage; otherwise optimistically render when authenticated.
• /webui/status route added in src/core/router/index.tsx.
• SignalR suppression (src/core/signalr/signalr.ts) — onreconnecting / onreconnected / onclose and requiresRestart are gated on serverLifecycle.action === 'idle', so StatusPage is the only UX during a user-initiated restart/shutdown.
• GeneralSettings handoff (src/pages/settings/tabs/GeneralSettings.tsx) — new Restart/Shutdown buttons (gated on CanRestart/CanShutdown) with ConfirmationPromptModal; onConfirmRestart/onConfirmShutdown dispatch setAction → mutate (Init/Restart, Init/Shutdown) → navigate('/webui/status').
• LoginPage redirect (src/pages/login/LoginPage.tsx) — any non-Started/non-Waiting state (or isError) redirects to /webui/status; removed the bespoke Starting/Failed blocks from the login UI.
• axios 401 fix (src/core/axios.ts) — fullPath now uses a proper /${url} slash, adds Settings exclusion (/api/v3/Settings) for the boot window so settings reads don't trigger a logout.
• Simplifications — detail destructure, !! truthiness checks, retry-interval consolidation, icon map, etc.
• Verified — pnpm lint and pnpm build pass; dev override removed before commit; a11y/aria removed per codebase conventions.

Testing

• pnpm lint and pnpm build pass.
• Manual restart / shutdown / starting flows verified end-to-end (StatusPage surfaces, redirects recover on Started).

[revam]

Got asked to review text, so reviewed text. My human findings are below. Rest of 'em seem fine-ish.