docs: add working with data guides

[frydj]

Summary

New Learn > Working with Data section with 6 guides:

• inserting-data.mdx: Creating entities with transactions
• updating-and-deleting-data.mdx: Modifying and removing data
• querying-basics.mdx: FlureeQL select/where fundamentals
• advanced-queries.mdx: Joins, subqueries, and graph traversal
• context-patterns.mdx: Practical @context usage patterns
• time-travel-and-history.mdx: Querying historical states

Test plan

• Verify examples are runnable against a Fluree instance
• Check progression from basics to advanced is logical

[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
• docs: add security guides #64
• docs: add modeling guides #63
• docs: add working with data guides #62 👈 (View in Graphite)
• docs: reorganize learn foundations #61
• docs: add getting started guides #60
• docs: add project config & infrastructure #59
• main

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