Rename backend code references: Bookmann → Bookhoard

Backend changes:
- Update import paths: bookmann/internal → bookhoard/internal
- Rename struct fields: BookmannUUID → BookhoardUUID
- Update handler function names: mapContentIdToBookmannUUID → mapContentIdToBookhoardUUID
- Update HTTP response headers: X-Bookmann-* → X-Bookhoard-*
- Update service and middleware references
- Update main.go imports and references

This is part 2 of the project rename to Bookhoard.

internal/handlers/sidecar.go

@@ -1,7 +1,7 @@
 package handlers
 
 import (
-	"bookmann/internal/database"
+	"bookhoard/internal/database"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -22,7 +22,7 @@ func NewSidecarHandler(db *database.Queries) *SidecarHandler {
 
 type SidecarConfig struct {
 	Version        string                 `json:"version"`
-	Bookmann       SidecarBookmannConfig  `json:"bookmann"`
+	Bookmann       SidecarBookmannConfig  `json:"bookhoard"`
 	Books          map[string]SidecarBook `json:"books"`
 	Collections    []SidecarCollection    `json:"collections"`
 	OPDSEnabled    bool                   `json:"opds_enabled"`
@@ -40,7 +40,7 @@ type SidecarBookmannConfig struct {
 }
 
 type SidecarBook struct {
-	BookmannUUID     string   `json:"bookmann_uuid"`
+	BookhoardUUID     string   `json:"bookhoard_uuid"`
 	Title            string   `json:"title"`
 	Author           string   `json:"author"`
 	AvailableFormats []string `json:"available_formats"`
@@ -119,7 +119,7 @@ func (h *SidecarHandler) GetSidecarConfig(c echo.Context) error {
 		}
 
 		books[key] = SidecarBook{
-			BookmannUUID:     bookUUID,
+			BookhoardUUID:     bookUUID,
 			Title:            item.Title,
 			Author:           author,
 			AvailableFormats: availableFormats,
@@ -254,7 +254,7 @@ func (h *SidecarHandler) DownloadSidecarConfig(c echo.Context) error {
 		}
 
 		books[key] = SidecarBook{
-			BookmannUUID:     bookUUID,
+			BookhoardUUID:     bookUUID,
 			Title:            item.Title,
 			Author:           author,
 			AvailableFormats: availableFormats,