Add introduction and loading message for Sudoku example page

[Copilot]

Adds documentation content and UX improvement to the Sudoku example page.

Changes

• Added introduction explaining the Sudoku solver and standard constraints (row, column, box)
• Added "How It Works" section describing the DS deductive system integration
• Added loading message displayed while JS resources are fetched

Before/After

Before: Empty page with just a header until Vue app loads

After: Introduction content visible immediately, with "Loading Sudoku Solver..." shown until the interactive demo initializes

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add introduction about the implementation and loading message for docs/examples/sudoku.md</issue_title>
<issue_description></issue_description>

<agent_instructions>Add introduction about sudoku in that page, and add a "loading" message before the related js loaded.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Add introduction about the implementation and loading message for docs/examples/sudoku.md #40

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