refactor(conflicts): one ConflictDetail builder for the three row shapes

ListConflicts, GetConflict, and the SSR media-detail active-conflict
lookup each hand-mapped their sqlc row (list-by-user, get-by-id,
list-by-media-item) into ConflictDetailResponse, triplicating the
optional resolution tail — including the silently-swallowed
ResolutionData unmarshal error, three times. NewConflictDetail is the
single mapper; a malformed resolution blob now logs instead of
vanishing.

Also extracts koreaderSyncEndpoints (the KOReader URL map duplicated
verbatim between token rotation and device approval; kobo's two URL
sets stay local because they deliberately differ).

Verified in the test-runner container (host conflict tests fail
environmentally on the container-only uploads path — baseline behavior).

internal/handlers/devices.go

@@ -217,6 +217,17 @@ func (h *DeviceHandler) CheckRegistrationStatus(c *echo.Context) error {
 	})
 }
 
+// koreaderSyncEndpoints is the KOReader endpoint map shared by the
+// surfaces that publish it (KOReader authenticates by header, so its
+// URLs never embed the token).
+func koreaderSyncEndpoints(baseURL string) map[string]string {
+	return map[string]string{
+		"progress":  fmt.Sprintf("%s/api/sync/koreader/progress", baseURL),
+		"metadata":  fmt.Sprintf("%s/api/sync/koreader/metadata", baseURL),
+		"bookmarks": fmt.Sprintf("%s/api/sync/koreader/bookmarks", baseURL),
+	}
+}
+
 // deviceToInfo is the single Devices->DeviceInfo mapper for every
 // device surface. AuthToken rides only on surfaces that deliberately
 // expose it (the owner's device lists).
@@ -483,9 +494,7 @@ func (h *DeviceHandler) RegenerateDeviceToken(c *echo.Context) error {
 		syncURLs["bookmark"] = fmt.Sprintf("%s/api/sync/kobo/%s/bookmark", baseURL, newToken)
 		syncURLs["init"] = fmt.Sprintf("%s/api/sync/kobo/%s/v1/initialization", baseURL, newToken)
 	case "koreader":
-		syncURLs["progress"] = fmt.Sprintf("%s/api/sync/koreader/progress", baseURL)
-		syncURLs["metadata"] = fmt.Sprintf("%s/api/sync/koreader/metadata", baseURL)
-		syncURLs["bookmarks"] = fmt.Sprintf("%s/api/sync/koreader/bookmarks", baseURL)
+		syncURLs = koreaderSyncEndpoints(baseURL)
 	}
 
 	// Handle HTMX requests - return HTML with page reload script
@@ -626,9 +635,7 @@ func (h *DeviceHandler) ApproveDevice(c *echo.Context) error {
 	syncEndpoints := map[string]string{}
 	switch registration.DeviceType {
 	case "koreader":
-		syncEndpoints["progress"] = fmt.Sprintf("%s/api/sync/koreader/progress", h.cfg.BaseURL)
-		syncEndpoints["metadata"] = fmt.Sprintf("%s/api/sync/koreader/metadata", h.cfg.BaseURL)
-		syncEndpoints["bookmarks"] = fmt.Sprintf("%s/api/sync/koreader/bookmarks", h.cfg.BaseURL)
+		syncEndpoints = koreaderSyncEndpoints(h.cfg.BaseURL)
 	case "kobo":
 		syncEndpoints["markup"] = fmt.Sprintf("%s/api/sync/kobo/markup", h.cfg.BaseURL)
 		syncEndpoints["library"] = fmt.Sprintf("%s/api/sync/kobo/library", h.cfg.BaseURL)