📚 Archivist: Clarify CI trigger conditions for prerelease builds

[2fst4u]

📚 Archivist: Clarify CI trigger conditions for prerelease builds

💡 Problem:
AGENTS.md incorrectly claimed that automatic prerelease dev builds were triggered by pushes to "any branch", including "direct main pushes". However, .github/workflows/build.yml contains a branches-ignore: - main clause and a paths-ignore block for markdown and workflow files, meaning the documentation was completely false regarding the main branch.

🎯 Fix:

• Updated the "Prerelease Builds (automatic)" text to explicitly note that the main branch, markdown files, and workflow files are ignored.
• Removed main from the dev branch tag example text.
• Removed "& direct main pushes" from the Docker Image Tags table.

🧪 Verification:

• Checked .github/workflows/build.yml triggers manually using cat.
• Formatted AGENTS.md and .jules/archivist.md with prettier.
• Ran make test to ensure no infrastructure tests (like test_release_config.py) were broken.

🔎 Scope:
This PR contains ONLY documentation changes to AGENTS.md and a new critical learning entry in .jules/archivist.md.

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PR created automatically by Jules for task 5190970421697098366 started by @2fst4u

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