Add DM inbox with NIP-04/NIP-17 support and soft delete

Features:
- Full DM inbox UI with conversation list and message view
- Support for both NIP-04 (kind 4) and NIP-17 (kind 14/1059) encryption
- Progressive message decryption with background loading
- Soft delete using kind 30078 Application Specific Data events
- Message selection UI with delete selected/delete all
- Undelete all functionality per conversation
- Jump to newest button with new message counter
- Conversation filtering (all / follows only)
- Per-conversation relay and encryption settings
- New messages indicator on sidebar (clears when inbox viewed)
- Follow indicator on conversation items

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/components/Sidebar/index.tsx

@@ -10,6 +10,7 @@ import { ChevronsLeft, ChevronsRight } from 'lucide-react'
 import AccountButton from './AccountButton'
 import BookmarkButton from './BookmarkButton'
 import HomeButton from './HomeButton'
+import InboxButton from './InboxButton'
 import LayoutSwitcher from './LayoutSwitcher'
 import NotificationsButton from './NotificationButton'
 import PostButton from './PostButton'
@@ -57,6 +58,7 @@ export default function PrimaryPageSidebar() {
         <HomeButton collapse={isCollapsed} />
         <NotificationsButton collapse={isCollapsed} />
         <SearchButton collapse={isCollapsed} />
+        {pubkey && <InboxButton collapse={isCollapsed} />}
         <ProfileButton collapse={isCollapsed} />
         {pubkey && <BookmarkButton collapse={isCollapsed} />}
         <SettingsButton collapse={isCollapsed} />