feat: Add public status page with 10-second polling

Implement status.corrosionmgmt.com public status page showcasing all
Corrosion servers that opt-in. Drives platform visibility and attracts
new customers.

Backend:
- Migration 007: status_page_description TEXT column
- models/public.rs: PublicServerStatus, PlatformHealth, StatusPageResponse
- db/public.rs: get_public_servers() with uptime calculations (24h/7d/30d)
- api/public.rs: GET /api/public/status (no auth)
- api/settings.rs: public site config endpoints (auth required)

Frontend:
- StatusPageView.vue: Server grid with live stats, uptime badges, wipe schedules
- Platform health header: total servers, online count, total players
- Auto-refresh every 10 seconds via polling
- Mobile-responsive design
- SettingsView.vue: Public Status tab with opt-in toggle

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/migrations/007_status_page_description.sql

@@ -0,0 +1,5 @@
+-- Add status_page_description column to public_site_config
+-- Supports custom server descriptions on the public status page
+
+ALTER TABLE public_site_config
+ADD COLUMN IF NOT EXISTS status_page_description TEXT;