TemplateEngineHelper: refactor formatting into pure functions + deterministic tests

[jongalloway]

The formatting/shape logic in TemplateEngine-related output is a good candidate for pure-function extraction.

Goals:

• Separate template discovery (SDK integration) from formatting/serialization logic.
• Enable deterministic unit tests for formatting without requiring Template Engine state.

Acceptance:

• Introduce pure formatting helpers (no I/O, no global/static state dependencies).
• Add unit tests validating formatting for representative template metadata.
• No behavior changes for tool outputs beyond whitespace/ordering only if explicitly intended.

Parent: #247