refactor(api): consolidate health check endpoints to /health

Removes the redundant `/healthz` and `/api/v1/health` endpoints, leaving `/health` as the sole health check endpoint.

- Update router to return 404 Not Found for the removed endpoints
- Update admin log filtering to only ignore `/health`
- Remove health URL from API documentation data
- Update tests to verify `/health` returns 200 and others return 404
- Update README documentation to reflect the change

backend/libs/handlers/api_docs.go

@@ -10,7 +10,6 @@ import (
 type apiDocsData struct {
 	BaseURL             string
 	UploadURL           string
-	HealthURL           string
 	RequestSchemaURL    string
 	ResponseSchemaURL   string
 	ShareXExamplePath   string
@@ -39,7 +38,6 @@ func (a *App) APIDocs(w http.ResponseWriter, r *http.Request) {
 		Data: apiDocsData{
 			BaseURL:             a.cfg.BaseURL,
 			UploadURL:           a.cfg.BaseURL + "/api/v1/upload",
-			HealthURL:           a.cfg.BaseURL + "/api/v1/health",
 			RequestSchemaURL:    a.cfg.BaseURL + "/api/v1/schemas/upload-request.json",
 			ResponseSchemaURL:   a.cfg.BaseURL + "/api/v1/schemas/upload-response.json",
 			ShareXExamplePath:   "examples/sharex/warpbox-anonymous.sxcu",