[cmanjah]

What does this PR do?

• Group Sphinx assets and shared code under source/, move content pages into pages/, and preserve old page URLs with redirects.
• Correct README build commands, contributor templates, narrative filenames, roadmap status, and navigation; add README badges.
• Keep unpublished Colab and Binder links out of exported catalogue data.
• Repair pre-commit file filters and the Windows requirements.txt line-ending conflict.

Part of #1

Type of change

• Infrastructure (gallery, scripts, CI)
• Documentation

Verification

• tests pass
• Schema and catalogue validation pass
• pre-commit run --all-files passes
• Clean no-execution Sphinx build passes with -W --keep-going
• No dataset files added

Follow-up

Notebook publishing and the scheduled executing build remain separate roadmap items. Launch actions stay disabled until notebook URLs are published and verified.