feat: custom user-defined template structure

[adamdaw]

Allow users to provide their own section structure as a YAML or Markdown template.

Context

Daedalus should be flexible enough for any documentation framework. A custom template mechanism would let users define their own sections, elicitation questions, and output format without modifying the core scripts.

Acceptance Criteria

• Template definition format (YAML with section names, questions, output format)
• make init supports TEMPLATE=path/to/custom.yaml
• Elicitation scripts read template definition dynamically
• Validation scripts adapt to custom section structure

Reference: docs/ENHANCEMENTS.md