feat: fix channel scanning bugs, add package tags, and kickstarters tab

Bug fixes:
- Fix channels not being scanned by paginating TDLib getChats (was only
  loading first batch, additional channels were unknown to TDLib)
- Add per-channel getChat pre-load as safety net before scanning
- Fix preview pictures not loading by checking previewData instead of
  previewMsgId for hasPreview flag
- Prevent previewMsgId from being set when preview download fails

Package Tags:
- Add tags Text[] column to Package with migration backfilling from
  channel categories
- Worker auto-inherits source channel category as initial tag
- Tag filter dropdown and Tags column in STL Files table
- Server actions for individual and bulk tag editing

Kickstarters Tab:
- New KickstarterHost, Kickstarter, and KickstarterPackage models
- Full CRUD with delivery status, payment status, host management
- Package linking (many-to-many with existing packages)
- Sidebar entry with Gift icon
- Table with search, filters, modal forms

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/constants.ts

@@ -7,6 +7,7 @@ export const NAV_ITEMS = [
   { label: "Paints", href: "/paints", icon: "Paintbrush", adminOnly: false },
   { label: "Supplies", href: "/supplies", icon: "Gem", adminOnly: false },
   { label: "STL Files", href: "/stls", icon: "FileBox", adminOnly: false },
+  { label: "Kickstarters", href: "/kickstarters", icon: "Gift", adminOnly: false },
   { label: "Telegram", href: "/telegram", icon: "Send", adminOnly: true },
   { label: "Invites", href: "/invites", icon: "UserPlus", adminOnly: true },
   { label: "Usage", href: "/usage", icon: "ClipboardList", adminOnly: false },