feat: support relations in templates

[OliverDudgeon]

Overview

This PR adds support for related items in Obsidian note templates, allowing users to access citation keys, backlinks, and relation metadata for connected Zotero items.

Addresses Issues:

• Addresses Relatation support #203: Related items support in templates
• Addresses Request for a field to retrieve related zotero items #312: Enhanced citation key handling for related content (not looked at the relations between notes that @asan-emirsaleh notes)

Relations in Templates

• relatedItems array: Full access to related items in template context
• Citation keys: Related items include relatedCiteKey for Better BibTeX integration
• Backlinks: Automatic zotero:// links for easy navigation to related items
• Relation metadata: Access to relation types and Zotero keys
• Cross-library support: Works with relations between user and group libraries

Template Example:

<%# Related Items Section %>
<%~ if (it.relatedItems && it.relatedItems.length > 0) { -%>
## Related Items

<%~ it.relatedItems.forEach(item => { -%>
- **<%~ item.relationType %>**: 
  <%~ if (item.relatedCiteKey) { -%>
    [[<%~ item.relatedCiteKey %>]] 
  <%~ } else { -%>
    <%~ item.relatedZoteroKey %>
  <%~ } -%>
  ([Open in Zotero](<%~ item.backlink %>))
<%~ }) -%>

<%~ } -%>

Implementation Details

Provides:

• relatedItems array in template context
• relatedCiteKey for Better BibTeX citation keys
• relatedZoteroKey for Zotero item keys
• relationType (e.g., "dc:relation", "owl:sameAs")
• backlink for direct Zotero navigation

Updated Data Structure:

{
  itemID: 230,
  relatedItemKey: "http://zotero.org/users/5370407/items/DKPQSMUT",
  relationType: "dc:relation",
  relatedZoteroKey: "DKPQSMUT",      // new: Extracted Zotero key
  relatedCiteKey: "author2023title", // new: Better BibTeX citation key
  backlink: "zotero://select/library/items/DKPQSMUT" // new: Direct link
}

Notes

This PR is unfinished as it removes compatibility with the old bbt database format. I was unfamiliar with the codebase and just cobelled something together that worked for me.

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Resolves: Template support for related items functionality
Partially addresses: #203 and #312 (related items in templates)
Type: Feature enhancement