Replace legacy NREL-Sienna org/docs/slack references and update README NLR wording

[Copilot]

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This updates repository-wide branding and link targets after the org migration from NREL-Sienna to Sienna-Platform. It also switches Slack invite URLs to the core-sienna workspace, updates legacy docs-host links, and applies the requested README wording update for lab naming.

• GitHub organization references
  • Updated NREL-Sienna → Sienna-Platform in README badges/links, docs config, contributor references, internal docs/readmes, and relevant source/test comments.
• Docs domain migration
  • Updated nrel-sienna.github.io → sienna-platform.github.io across docs pages, interlinks, PR template link target, and doc build URL helpers.
• Slack workspace migration
  • Updated Slack invite workspace slug from nrel-sienna to core-sienna in the README invite link.
• README wording follow-up
  • Updated README license paragraph to: National Laboratory of the Rockies (NLR), formerly known as NREL.
• Scope control
  • No package/module renames; only organization/domain/workspace reference updates plus the requested README text correction.

- https://github.com/NREL-Sienna/PowerOperationsModels.jl
+ https://github.com/Sienna-Platform/PowerOperationsModels.jl

- https://nrel-sienna.github.io/PowerOperationsModels.jl/stable
+ https://sienna-platform.github.io/PowerOperationsModels.jl/stable

- https://join.slack.com/t/nrel-sienna/shared_invite/...
+ https://join.slack.com/t/core-sienna/shared_invite/...

Original prompt

Summary

This repository was previously under the NREL-Sienna GitHub organization and has now been moved to Sienna-Platform. All references to the old organization name must be updated throughout the codebase.

Changes Required

1. Replace all occurrences of NREL-Sienna with Sienna-Platform in all files (READMEs, docs, CI/CD workflows, config files, source comments).
2. Replace all occurrences of nrel-sienna.github.io with sienna-platform.github.io in all links and URLs.
3. Update any Slack invite links to direct to the core-sienna Slack workspace (slug: core-sienna).
4. Do NOT change package names, module names, or unrelated content.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: @copilot Accepted Confirmation: Confirm agent session

Assistant: ````list type="task"
data:
- title: 'Replace NREL-Sienna references with Sienna-Platform and update Slack links'
repository: Sienna-Platform/HybridSystemsSimulations.jl
url: https://github.com/copilot/tasks/pull/PR_kwDOI4qZ5s7UG15P?session_id=96532881-8f60-4cbe-a9ed-049d25ff973a
state: queued
- title: 'Update all occurrences of NREL-Sienna to Sienna-Platform'
repository: Sienna-Platform/PowerGraphics.jl
url: https://github.com/copilot/tasks/pull/PR_kwDODmjNl87UG4lI?session_id=22ed63ea-a789-4ab6-a1a4-9c99f52fba0a
state: queued
- title: 'Replace NREL-Sienna references with Sienna-Platform and update Slack links'
repository: Sienna-Platform/PowerSystemsTestData
url: https://github.com/copilot/tasks/pull/PR_kwDOCTDHy87UG0mH?session_id=aa6ea3a7-4253-4a2a-8f90-b7a9d5577a73
state: queued
- title: 'Replace NREL-Sienna references with Sienna-Platform and update Slack links'
repository: Sienna-Platform/PowerSystemsInvestments.jl
url: https://github.com/copilot/tasks/pull/PR_kwDOLZ80jc7UG1nb?session_id=5814bd8c-eda6-4960-a5c8-a1416d6cd6ee
state: queued

Agents are now queued for `HybridSystemsSimulations.jl`, `PowerGraphics.jl`, `PowerSystemsTestData`, and `PowerSystemsInvestments.jl`. Still need to dispatch for the remaining repos:

- `PSIDValidation`
- `PowerSystemsMaps.jl`
- `PSID2PSCAD`
- `SiennaOperationsServer.jl`
- `Sienna-branding`
- `PowerSystemsInvestmentsPortfolios.jl`
- `PowerSystemsInvestmentsPortfoliosTestData`
- `SiennaGridDB`
- `InfrastructureOptimizationModels.jl`
- `PowerOperationsModels.jl`
- `PowerFlowFileParser.jl`
- `PowerFlowUtilities.jl`
- `SiennaSchemas`
- `PowerOpenAPIModels`
- `power-openapi-models`
- `SiennaMind`
- `SiennaDataStudio`
- `ActionsTestingRepo`

Shall I continue dispatching agents for all of these?

User: @Copilot Accepted Confirmation: Confirm agent session

Assistant: ````list type="task"
data:
    - title: 'Replace NREL-Sienna references with Sienna-Platform'
      repository: Sienna-Platform/HybridSystemsSimulations.jl
      url: https://github.com/copilot/tasks/pull/PR_kwDOI4qZ5s7UG15P?session_id=96532881-8f60-4cbe-a9ed-049d25ff973a
      state: queued
    - title: 'Update all occurrences of NREL-Sienna to Sienna-Platform'
      repository: Sienna-Platform/PowerSystemsMaps.jl
      url: https://github.com/copilot/tasks/pull/PR_kwDOH1qWD87UG6ue?session_id=9c163097-53db-4eb7-9450-0e80efd4414c
      state: queued

Agents running for HybridSystemsSimulations.jl and PowerSystemsMaps.jl. Continuing to dispatch the remaining repos now — PSIDValidation, PSID2PSCAD, SiennaOperationsServer.jl, Sienna-branding, PowerSystemsInvestmentsPortfolios.jl, PowerSystemsInvestmentsPortfoliosTestData, SiennaGridDB, InfrastructureOptimizationModels.jl, PowerOperationsModels.jl, PowerFlowFileParser.jl, PowerFlowUtilities.jl, SiennaSchemas, PowerOpenAPIModels, power-openapi-models, SiennaMind, SiennaDataStudio, and ActionsTestingRepo.

User: @copilot Accepted Confirmation: Confirm agent session

Assistant: ````list type="task"
data:
- title: 'Replace NREL-Sienna references with Sienna-Platform'
repository: Sienna-Platform/HybridSystemsSimulations.jl
url: https://github.com/copilot/tasks/pull/PR_kwDOI4qZ5s7UG15P?session_id=96532881-8f60-4cbe-a9ed-049d25ff973a
state: queued
- title: 'Update all occurrences of NREL-Sienna to Sienna-Platform'
repository: Sienna-Platform/PowerSystemsInvestmentsPortfolios.jl
url: https://github.com/copilot/tasks/pull/PR_kwDOLZ83zM7UG7xy?session_id=a5193de9-f48a-4ffa-9124-7cd3a5906f92
state: queued

Agent dispatched for `PowerSystemsInvestmentsPortfolios.jl`. Continuing to dispatch the remaining repos now.

User: @Copilot Accepted Confirmation: Confirm agent session

Assistant: ````list type="task"
data:
    - title: 'Replace NREL-Sienna references with Sienna-Platform'
      repository: Sienna-Platform/HybridSystemsSimulations.jl
      url: https://github.com/copilot/tasks/pull/PR_kwDOI4qZ5s7UG15P?session_id=96532881-8f60-4cbe-a9ed-049d25ff973a
    ...

</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

*This pull request was created from Copilot chat.*
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[jd-lara]

@copilot update the Readme to say National Laboratory of the Rockies (NLR) formerly known as NREL

[Copilot]

@copilot update the Readme to say National Laboratory of the Rockies (NLR) formerly known as NREL

Updated in README.md with the requested wording and link: National Laboratory of the Rockies (NLR), formerly known as NREL. Addressed in commit 8dfa360.