Add multi-repo-branching preset to community catalog (#2139)

* Add nested-repos to community catalog

- Preset ID: nested-repos
- Version: 1.0.0
- Author: sakitA
- Description: Multi-module nested repository support for independent repos and git submodules

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Update presets/catalog.community.json

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Bump catalog updated_at timestamp

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Update nested-repos preset: commands-only, 0 templates

Removed template overrides to reduce core content duplication.
Commands instruct AI to add nested-repo sections dynamically.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Rename preset: nested-repos -> multi-repo-branching

Updated preset ID, name, description, and all URLs to reflect
the new repository name and clearer preset identity.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Remove templates: 0 from catalog provides section

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Remove accidentally committed .claude folder

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review: restore templates key and add README entry

- Add templates: 0 back to provides for catalog consistency
- Add multi-repo-branching to Community Presets table in README.md

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>