docs(examples): unify Linux/Windows run blocks into single code block

[galuszkm]

Description

Collapse split ### Linux / macOS + ### Windows subsections into a single bash code block with # Linux / macOS and # Windows PowerShell comment headers, matching the style used in the configuration docs.

Also replace all Windows backslash paths with forward-slash equivalents — PowerShell and Python both accept POSIX paths on Windows, so no separate path variants are needed.

Affects: TEMPLATE_EXAMPLE.md, 02_vars_and_anchors/README.md, 11_multi_file_config/README.md

Related Issues

N/A

Type of Change

• Documentation update

YAML / API Impact

N/A

Testing

How have you tested the change?

• I ran uv run just check (lint + type check)
• I ran uv run just test for overall testing
• I added or updated tests that prove my fix is effective or my feature works
• I verified existing examples in examples/ still work

Checklist

• I have read the CONTRIBUTING document
• I have updated the documentation accordingly
• My changes generate no new warnings
• Any dependent changes have been merged and published

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