Improve overload-set documentation

[alandefreitas]

Overload pages list signatures and merged parameters, but lack a structured narrative. Readers cannot easily tell how overloads differ.

Proposed solution

• Investigate strategies such as (a) common paragraphs plus numbered overload-specific notes, (b) selecting a base overload and layering differences, or (c) dedicated commands in the markup.
• Prototype configuration options so projects can pick the strategy they prefer.
• Update post-processing steps to support the chosen strategy.
• Consider parser work to detect common paragraphs automatically.

Requirements

• Document the proposed strategy with examples.
• Implementation plan identified (including template changes).
• Tests cover at least one overload set using the new behavior.