Refactor load testing scripts to support Bash and PowerShell

- Updated README.md to reflect changes in load testing commands and added usage examples for Bash scripts.
- Converted PowerShell load testing scripts to Bash equivalents for better cross-platform compatibility.
- Added new Bash scripts: run-loadtests.sh, summarize-artillery.sh, and summarize-k6.sh to mirror existing PowerShell functionality.
- Updated admin-api.js and ws-chat.yml for consistency and improved performance metrics reporting.
- Enhanced error handling and output formatting in summary scripts for better readability.

README.md

@@ -213,11 +213,13 @@ One-off and CI-friendly scripts for video preparation, R2 sync, backups, and pla
 
 - loadtest/
   - [admin-api.js](scripts/loadtest/admin-api.js) — admin API load test script
-  - [run-loadtests.ps1](scripts/loadtest/run-loadtests.ps1) — PowerShell script to run load tests
-  - [summarize-artillery.ps1](scripts/loadtest/summarize-artillery.ps1) — PowerShell script to summarize Artillery load test results
-  - [summarize-k6.ps1](scripts/loadtest/summarize-k6.ps1) — PowerShell script to summarize k6 load test results
+  - [run-loadtests.sh](scripts/loadtest/run-loadtests.sh) — bash script to run ws and/or admin load tests
+  - [summarize-artillery.sh](scripts/loadtest/summarize-artillery.sh) — summarize Artillery JSON results
+  - [summarize-k6.sh](scripts/loadtest/summarize-k6.sh) — summarize k6 JSON results
   - [ws-chat.yml](scripts/loadtest/ws-chat.yml) — WebSocket chat load test configuration
 
+  PowerShell equivalents (`*.ps1`) of the three load-test scripts are kept alongside them.
+
 ## Getting Started
 
 > **Note:** The `docker compose up` below targets local development. The test lab (192.168.88.40) receives automated CD deploys. Production Hetzner VPS is not yet provisioned — see `DEPLOYMENT.md`.