feat: content tab rewrite for worlds

[IMB11]

Summary

• Standardizes the content management layout into a single shared ContentPageLayout component used by both the app frontend (Mods.vue) and hosting frontend (content.vue), eliminating duplicated UI code
• Introduces a ContentManagerContext dependency injection provider that decouples platform-specific API logic from the shared layout
• Gates the new v1 hosting content API (with bulk operations) behind a useV1ContentTabAPI feature flag, allowing the old v0 file-based API to remain as the default for now

Content page layout (ContentPageLayout.vue)

Previously, the app's Mods.vue and hosting's content.vue each maintained their own implementations of the content management UI (search, filters, sorting, bulk actions, modpack card, empty states, confirmation modals, etc.). This PR extracts all of that into a single ContentPageLayout component in @modrinth/ui (~774 lines).

The layout consumes its data and actions entirely through dependency injection rather than props, so platform-specific pages only need to provide their handlers via provideContentManager() and then render <ContentPageLayout />.

Shared composables were also extracted into packages/ui/src/composables/content/:

• useContentSearch - fuzzy search via Fuse.js
• useContentFilters - dynamic filter pills (by type, updates, disabled)
• useContentSelection - multi-select state
• useBulkOperation - progress tracking with navigation guards
• useChangingItems - per-item loading states

Dependency injection (ContentManagerContext)

A new DI provider at packages/ui/src/providers/content-manager.ts defines the contract between ContentPageLayout and its platform-specific implementations. The context includes:

• Required: items, loading, error, refresh, toggleEnabled, deleteItem, browse, uploadFiles, mapToTableItem
• Optional (platform-specific): bulkDeleteItems, bulkEnableItems, bulkDisableItems (hosting v1 only), updateItem, bulkUpdateItem, hasUpdateSupport (app only), shareItems, getOverflowOptions, uploadState, modpack actions

This means the app's Mods.vue provides Tauri-backed handlers with update/share/export support, while hosting's content.vue provides API-backed handlers with optional bulk operations - all feeding into the same layout.

Feature flags (v0/v1 content API)

A useV1ContentTabAPI feature flag in apps/frontend/src/composables/featureFlags.ts controls which hosting content API is used:

• v0 (default): File-based operations via archon.content_v0 - individual toggle/delete calls that rename files with .disabled suffix
• v1 (flag-enabled): Database-backed operations via archon.content_v1 - supports bulk enable/disable/delete endpoints, modpack unlinking, and the new addon model

The hosting content.vue page maintains dual query instances (only one enabled at a time) and conditionally provides bulk operation handlers to the layout only when v1 is active. The flag is passed as a prop from the page wrapper: <ServersManageContentPage :use-v1-api="flags.useV1ContentTabAPI" />.

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Frontend previews

Last deployed commit is eb5a8358ed394e82fe150ba2fd09abf7fee3f06d

Environment	URL
staging	https://git-eb5a8358-frontend-staging.modrinth.workers.dev
production	https://git-eb5a8358-frontend.modrinth.workers.dev