docs: add advanced topics

[frydj]

Summary

New Learn > Advanced Topics section with 4 guides:

• calculated-transactions.mdx: Computed values and transaction functions
• language-tags.mdx: Multilingual data with @language
• architecture-overview.mdx: (moved from foundations/) System architecture
• collaborative-data.mdx: (moved from tutorial/) Multi-party data sharing

Removed

• tutorial/fluree-data-model.mdx: Content restructured into other guides
• tutorial/introduction.md: Replaced by getting-started section

Test plan

• Verify calculated transaction examples work
• Check architecture diagrams are current

[frydj]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• docs: add feature showcase examples #71
• docs: add domain example datasets #70
• docs: add feature reference docs #69
• docs: reorganize cookbook #68
• docs: restructure querying reference #67
• docs: restructure HTTP API reference #66
• docs: add advanced topics #65 👈 (View in Graphite)
• docs: add security guides #64
• docs: add modeling guides #63
• docs: add working with data guides #62
• docs: reorganize learn foundations #61
• docs: add getting started guides #60
• docs: add project config & infrastructure #59
• main

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