feat: allow non-owners to propose project changes #1

Without this patch, only project owners could edit project information,
preventing community contributions to improve project data accuracy.

This is a problem because users who want to help improve project
information or suggest corrections cannot contribute, limiting the
collaborative potential of the platform.

This patch solves the problem by implementing a proposal system where
authenticated users can suggest changes to any project. When a non-owner
makes edits, changes are saved as proposal records in their own repository
under the org.impactindexer.proposal collection, while owner edits continue
to update the original project directly. The UI provides clear indicators
showing when changes are proposals versus direct edits, and success messages
differentiate between the two modes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>