Add changelog workflows

[lcawl]

Summary

Created the three caller workflows under .github/workflows/:

File	Role
changelog-validate.yml	PR gate → docs-actions validate with config: changelog.yml
changelog-submit.yml	workflow_run on changelog-validate → submit with write/OIDC perms
changelog-upload.yml	Push to main → upload with OIDC perms

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: Cursor Grok 4.5

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