feat(ui): split book-card play action into reader/detail routing

The play button on book cards now opens the reader directly, instead of
always going to the detail page. Cards with an active progress sync
conflict route the play button to the detail page (which hosts the
conflict dialogue and resolves before writing progress), so the user is
never silently dropped into the reader with an unresolved conflict.

Backend:
- Add HasConflict to BookInfo and stamp it via ListSyncConflictsByUser
  (MarkActiveConflicts / MarkActiveConflictsSections) on the dashboard,
  bookshelf, series, tag, and search result card builders.
- Each page issues a single conflict query regardless of card count.

BookCard:
- Restructure into a detail link (cover + meta) with the play action as a
  sibling overlay using a pointer-events split: the container passes
  clicks through to detail while only the circular button routes to the
  reader. No nested anchors.
- On touch devices (hover: none) the play button stays visible.

Fix: carousel nav buttons had opacity-0 without pointer-events-none, so
they swallowed hover/clicks over book cards on the dashboard. They are
now click-through until the carousel is hovered.

internal/handlers/dashboard.go

@@ -4,6 +4,7 @@ import (
 	"bookhoard/internal/database"
 	"bookhoard/internal/services"
 	"bookhoard/internal/utils"
+	"context"
 	"log"
 	"net/http"
 	"strconv"
@@ -188,6 +189,59 @@ func BuildSections(sections []services.DashboardSection, currentLibraryID string
 	return result
 }
 
+// activeConflictSet returns the set of media item IDs (as strings) that have an
+// active (unresolved) progress sync conflict for the given user. A single query
+// is issued; resolved conflicts are filtered out in memory.
+func activeConflictSet(ctx context.Context, db *database.Queries, userID pgtype.UUID) map[string]bool {
+	conflicts, err := db.ListSyncConflictsByUser(ctx, userID)
+	if err != nil {
+		return nil
+	}
+	set := make(map[string]bool, len(conflicts))
+	for _, c := range conflicts {
+		if c.ResolutionStatus.String == "unresolved" {
+			set[uuid.UUID(c.MediaItemID.Bytes).String()] = true
+		}
+	}
+	return set
+}
+
+// MarkActiveConflicts stamps HasConflict on each book whose media item has an
+// active progress sync conflict for the user. It performs a single query
+// regardless of how many books are passed.
+func MarkActiveConflicts(ctx context.Context, db *database.Queries, userID pgtype.UUID, books []BookInfo) []BookInfo {
+	if len(books) == 0 {
+		return books
+	}
+	set := activeConflictSet(ctx, db, userID)
+	for i := range books {
+		if set[books[i].MediaItemID] {
+			books[i].HasConflict = true
+		}
+	}
+	return books
+}
+
+// MarkActiveConflictsSections is the section-aware variant of MarkActiveConflicts,
+// used by the dashboard which renders books grouped into sections.
+func MarkActiveConflictsSections(ctx context.Context, db *database.Queries, userID pgtype.UUID, sections []SectionData) []SectionData {
+	if len(sections) == 0 {
+		return sections
+	}
+	set := activeConflictSet(ctx, db, userID)
+	if len(set) == 0 {
+		return sections
+	}
+	for s := range sections {
+		for i := range sections[s].Items {
+			if set[sections[s].Items[i].MediaItemID] {
+				sections[s].Items[i].HasConflict = true
+			}
+		}
+	}
+	return sections
+}
+
 func getViewAllURL(collectionID string, libraryID string) string {
 	if collectionID != "" {
 		if libraryID != "" {