feat: add book detail page with comprehensive metadata display

Implement SSR-first book detail page at /media/:uuid with complete
book information, progress tracking, and interactivity.

Features:
- Cover image (256x384px) with responsive layout
- Complete metadata: title, author, description, publisher, ISBN,
  language, edition, page count, genre, copyright year, format
- External service links (Goodreads, Open Library, Google Books, Amazon)
  with smart URL fallback: ID → ISBN → Title+Author
- Reading progress display with device sources (web/kobo/koreader)
- Sync progress modal for conflict resolution
- Collections display as clickable badges
- Notes/highlights counter with placeholder modal
- Rating display (1-10 scale with star rendering)
- HTML sanitization for book descriptions using bluemonday

Data Structure:
- handlers.MediaDetail embeds database.MediaItems for zero duplication
- Uses existing database queries (GetMediaItem, GetMediaRating, etc.)
- Follows project pattern: no parallel type systems

Frontend:
- TypeScript modal triggers (book-detail.ts)
- Alpine.js for modal interactions
- TailwindCSS styling with theme variables
- Responsive: cover-left layout, mobile stacks vertically

Backend:
- Route: GET /media/:uuid (protected)
- Handler: inline function in frontend.go following existing pattern
- Template: SSR-first with progressive enhancement
- Returns HTML only (API uses separate /api/media-items/:id endpoint)

Files created:
- internal/handlers/media_detail.go
- templates/book_detail.templ
- templates/book_detail_modals.templ
- web/src/book-detail.ts

Files modified:
- internal/router/frontend.go (add route)
- web/src/main.ts (import module)

internal/handlers/media_detail.go

@@ -0,0 +1,21 @@
+package handlers
+
+import "bookhoard/internal/database"
+
+// MediaDetail embeds database.MediaItems for complete book metadata
+// No field duplication - template gets direct access to all database fields
+type MediaDetail struct {
+	database.MediaItems // Embedded - ALL book fields available
+
+	// User-specific data
+	Rating          *database.MediaRatings    `json:"rating,omitempty"`
+	Collections     []database.Collections    `json:"collections"`
+	ReadingProgress *database.ReadingProgress `json:"reading_progress,omitempty"`
+
+	// Conflict data (if exists)
+	ActiveConflict *ConflictDetailResponse `json:"active_conflict,omitempty"`
+
+	// Computed counts
+	NotesCount      int `json:"notes_count"`
+	HighlightsCount int `json:"highlights_count"`
+}