Update documentation for schema view and navigation changes

[kmcginnes]

Description

Updates the features documentation and README to reflect recent UI changes.

• Add Schema Explorer to the features list in the README
• Update Data Explorer description in the README to mention export capability
• Rename "Graph Explorer UI" to "Graph View" to match current navigation
• Rename "Data Explorer UI" to "Data Table View" to match current navigation
• Update navigation instructions to reference the navigation bar instead of top-right buttons
• Replace curly quotes with standard quotes for consistency
• Update "graph data model type" to "query language" to match current terminology
• Add link to GitHub discussions in the roadmap reference
• Add full documentation section for the new Schema View feature, including a note that the schema is inferred from query samples and grows over time

Validation

Documentation-only changes. Reviewed for accuracy against the current UI.

Related Issues

• Part of [Roadmap] Schema Visualization #685

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0
  license.
• I have run pnpm checks to ensure code compiles and meets standards.
• I have run pnpm test to check if all tests are passing.
• I have covered new added functionality with unit tests if necessary.
• I have added an entry in the Changelog.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.77%. Comparing base (c5affc5) to head (b74065d).
⚠️ Report is 77 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1545       +/-   ##
===========================================
+ Coverage   47.81%   64.77%   +16.96%     
===========================================
  Files         382      365       -17     
  Lines        8525     8299      -226     
  Branches     3159     3100       -59     
===========================================
+ Hits         4076     5376     +1300     
+ Misses       3070     2074      -996     
+ Partials     1379      849      -530     

Flag	Coverage Δ
unittests	64.77% <ø> (+16.96%)	⬆️

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