Refactor handlers and update changelog for 5.0.0-Beta

- Split IndexHandler into HealthHandler, VersionHandler, and CharacterHandler
- Rename index.go to version.go in backend
- Change VersionData.Changelog from string to []string
- Add changelog entries for issues #16-#23
- Remove TestDB function and related code
- Fix import ordering in several files

Closes #21, #22
References #16, #17, #18, #19, #20, #23

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/server/versionHandler.go

@@ -0,0 +1,51 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/labstack/echo/v5"
+	"music-server/internal/backend"
+)
+
+type VersionHandler struct {
+}
+
+func NewVersionHandler() *VersionHandler {
+	return &VersionHandler{}
+}
+
+// GetVersionHistory godoc
+//
+//	@Summary		Getting the version history of the backend
+//	@Description	get version history
+//	@Tags			version
+//	@Accept			json
+//	@Produce		json
+//	@Success		200	{array}	backend.VersionData
+//	@Failure		404	{object}	string
+//	@Router			/version/history [get]
+func (v *VersionHandler) GetVersionHistory(ctx *echo.Context) error {
+	versionHistory := backend.GetVersionHistory()
+	if len(versionHistory) == 0 {
+		return ctx.JSON(http.StatusNotFound, "version not found")
+	}
+	return ctx.JSON(http.StatusOK, versionHistory)
+}
+
+// GetLatestVersion godoc
+//
+//	@Summary		Getting the latest version of the backend
+//	@Description	get latest version info
+//	@Tags			version
+//	@Accept			json
+//	@Produce		json
+//	@Success		200	{object}	backend.VersionData
+//	@Failure		404	{object}	string
+//	@Router			/version [get]
+func (v *VersionHandler) GetLatestVersion(ctx *echo.Context) error {
+	latestVersion := backend.GetLatestVersion()
+	if latestVersion.Version == "" {
+		return ctx.JSON(http.StatusNotFound, "version not found")
+	}
+	return ctx.JSON(http.StatusOK, latestVersion)
+}