Document pipeline operator semantics and precedence. Closes #24

[binaek]

Summary

• Adds a standalone pipeline operator reference page with complete syntax and behavior details.
• Keeps functions and top-level reference docs concise by linking to the dedicated page.
• Preserves existing guidance on precedence, desugaring, memoization, and use/resolution boundaries in a single canonical location.

Changes

• Added src/content/docs/reference/pipeline-operator.md:
  • comprehensive page for |> syntax, desugaring, supported/rejected targets, precedence/associativity, memoization, and resolution semantics.
• Updated src/content/docs/reference/functions.md:
  • replaced the long inline pipeline section with a short introduction and a pointer to the dedicated pipeline reference page.
• Updated src/content/docs/reference/index.md:
  • added a table-of-contents link to the dedicated pipeline page and simplified the pipeline operator subsection.

Testing

• Documentation-only change; verified markdown consistency and internal links for the new dedicated page layout.

[github-actions]

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