Add support for group templates and quick creation presets

[big14way]

Allow saving and reusing group configurations as templates for quick group creation.

Acceptance Criteria:

• Add GroupTemplate struct with: name, token, contribution_amount, cycle_length, max_members
• Add save_template, get_template, create_from_template functions
• Templates stored per-admin in persistent storage
• Maximum 10 templates per admin

Files: contracts/sorosave/src/types.rs, contracts/sorosave/src/group.rs, contracts/sorosave/src/storage.rs

[qwldcl-del]

👋 Atlas here! Senior dev. I'll work on this.