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/characterHandler.go

@@ -0,0 +1,42 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/labstack/echo/v5"
+	"music-server/internal/backend"
+)
+
+type CharacterHandler struct {
+}
+
+func NewCharacterHandler() *CharacterHandler {
+	return &CharacterHandler{}
+}
+
+// GetCharacterList godoc
+// @Summary Get list of characters
+// @Description Returns a list of all available characters
+// @Tags characters
+// @Accept json
+// @Produce json
+// @Success 200 {array} string
+// @Router /characters [get]
+func (c *CharacterHandler) GetCharacterList(ctx *echo.Context) error {
+	characters := backend.GetCharacterList()
+	return ctx.JSON(http.StatusOK, characters)
+}
+
+// GetCharacter godoc
+// @Summary Get character image
+// @Description Returns the image for a specific character
+// @Tags characters
+// @Accept json
+// @Produce image/png
+// @Param name query string true "Character name"
+// @Success 200 {file} file
+// @Router /character [get]
+func (c *CharacterHandler) GetCharacter(ctx *echo.Context) error {
+	character := ctx.QueryParam("name")
+	return ctx.File(backend.GetCharacter(character))
+}