QoL fixes, UI rework, mobile improvements & provider health checks

[Quickkill0]

Summary

Extracted QoL/UI improvements and bug fixes from the multi-user PR, with all auth/user-management code removed. This is a standalone set of improvements that works on the existing codebase with no new dependencies.

Backend

• Provider health checks: per-provider, per-package, and all-providers health check system with DB persistence
• Download management: remove single download, clear by status, retry all failed
• Search improvements: per-provider augment timeouts (30s), cancellation handling, batch thumb registration
• Provider cache resilience: thread-safe semaphore, try-catch around broken extensions at startup
• Series fixes: route rename /api/serie → /api/series, rename files endpoint, title correction fixes
• EF migration for provider health check columns

Frontend

• Sidebar redesign: expandable/collapsible with pin, theme toggle, inline download counters, framer-motion animations
• Mobile header: hamburger menu, swipe-from-left gesture, responsive search overlay
• Queue page redesign: tabbed UI (Running/Waiting/Completed/Failed), metrics summary bar, confirm dialogs, bulk actions
• Series detail: compact ProviderCard layout with small thumbnails and badges
• Cloud latest: responsive details modal (drawer on mobile, dialog on desktop)
• Provider manager: health check buttons with status badges and tooltips
• PWA support: service worker, offline page, install prompt, web manifest
• New UI components: pull-to-refresh, responsive-modal, textarea, FAB, shared PageLayout
• Settings: tabbed UI with General and About tabs
• API client: better error message parsing from response body, abort signal support
• SignalR: guard against concurrent connection initialization

Build/CI

• Docker build: JDK 21 + Gradle for Android.Compat.dll rebuild step
• Standalone rebuild-androidcompat workflow
• Bridge runtime improvements and ExtensionLoadException

What's NOT included

• No user/auth system (JWT, login, registration, permissions, invites, requests)
• No new NuGet dependencies (BCrypt, JwtBearer, JWT tokens)
• No [Authorize] attributes on controllers
• No database schema changes for users/sessions/permissions

Test plan

• Verify app starts and provider cache loads (with resilience for broken extensions)
• Test sidebar expand/collapse/pin and theme toggle
• Test queue page tabs, metrics, clear/retry-all actions
• Test provider health check from provider manager
• Test search with cancellation (navigate away during search)
• Test download management (remove single, clear completed/failed)
• Test series rename button on series detail page
• Verify mobile responsiveness (hamburger, swipe, drawer modals)
• Test PWA install prompt and offline page