[Feature Request] Support Assigning a Canvas to Multiple Knowledge Bases

Is your feature request related to a problem? Please describe.

Currently, a canvas can only belong to a single knowledge base. This limitation becomes problematic when a canvas contains content relevant to multiple topics or knowledge bases. For example, a design system canvas might apply to both "UI Components" and "Design Patterns" knowledge bases, but the user is forced to choose only one, making organization less flexible.

Describe the solution you'd like

Allow a canvas to be assigned to multiple knowledge bases, similar to a multi-tagging or multi-category system. This would:

• Enable better content organization by reflecting real-world cross-disciplinary use cases.
• Maintain the advanced features of knowledge bases (e.g., retrieval/recall) while improving flexibility.

Describe alternatives you've considered

1. Manual duplication: Copying the canvas into multiple knowledge bases, but this creates sync issues.
2. Symbolic links: A technical workaround, but not user-friendly.
3. Folders + knowledge bases: Using folders for broad categorization and knowledge bases for advanced retrieval, but this adds complexity without solving the core problem.

Additional context

• Knowledge bases act as "smarter folders" with enhanced capabilities (e.g., semantic search).
• UI/UX considerations: How to visually indicate multi-assignment (e.g., tags, dropdown checkboxes).

Looking forward to your thoughts and collaboration on this!

Start by tracing how a canvas currently belongs to one knowledge base and how knowledge-base retrieval or recall uses that relationship. Review the assignment UI, including the proposed tags or dropdown checkboxes, and define done as one canvas being selectable in multiple knowledge bases without duplication while preserving retrieval and recall.