Keep deployment logs findable after the container is recreated (closes #214)

Deployment log files were stored under a directory named after the
container's hostname, which Docker changes whenever the container is
recreated, so every older log download returned 404. Logs now live under
logs/<appname>/. The download handler still finds logs written by older
versions under any hostname directory.

Model: opus-5-5

internal/service/deploy/deploy.go

@@ -261,15 +261,14 @@ func (svc *Service) GetBuildDir(appName string) string {
 
 // GetLogFilePath returns the path to the log file for a deployment.
 // Returns empty string if the path cannot be determined.
+//
+// The path must not depend on the container's hostname: Docker assigns a
+// new one whenever the container is recreated, and older logs would then
+// no longer be found.
 func (svc *Service) GetLogFilePath(
 	app *models.App,
 	deployment *models.Deployment,
 ) string {
-	hostname, err := os.Hostname()
-	if err != nil {
-		hostname = "unknown"
-	}
-
 	// Get commit SHA
 	sha := ""
 	if deployment.CommitSHA.Valid && deployment.CommitSHA.String != "" {
@@ -291,7 +290,7 @@ func (svc *Service) GetLogFilePath(
 		filename = fmt.Sprintf("%s_%s.log.txt", app.Name, timestamp)
 	}
 
-	return filepath.Join(svc.config.DataDir, "logs", hostname, app.Name, filename)
+	return filepath.Join(svc.config.DataDir, "logs", app.Name, filename)
 }
 
 // GetLogDir returns the root directory under which all deployment log
@@ -1294,7 +1293,7 @@ func (svc *Service) failDeployment(
 }
 
 // writeLogsToFile writes the deployment logs to a file on disk.
-// Structure: DataDir/logs/<hostname>/<appname>/<appname>_<sha>_<timestamp>.log.txt
+// Structure: DataDir/logs/<appname>/<appname>_<sha>_<timestamp>.log.txt
 func (svc *Service) writeLogsToFile(app *models.App, deployment *models.Deployment) {
 	if !deployment.Logs.Valid || deployment.Logs.String == "" {
 		return