Context

Templates currently are standalone YAML files. This issue adds inheritance/composition so templates can extend others (e.g., startup extends solo_founder by adding more agents).

Acceptance Criteria

• `extends: <template_name>` directive in template YAML
• Agent merging strategy (child adds to parent agents, can override by role)
• Department merging strategy (child adds/overrides parent departments)
• Variable inheritance (child inherits parent variables, can add/override)
• Config inheritance (child overrides parent budget, autonomy, etc.)
• Circular inheritance detection and clear error messages
• Multi-level inheritance (A extends B extends C)
• Unit tests

Dependencies

• Issue Define default configurations and company template schema #60 (company template schema)

Design Spec Reference

Inspired by Jinja2 template inheritance and Helm chart dependencies