Problem

Template inheritance is fully implemented and tested (#84, closed) but zero builtin templates use extends. Each template duplicates its entire agent roster, department structure, and config -- even when templates are natural progressions of each other (solo_founder -> startup -> dev_shop).

Proposed Changes

Restructure builtins into an inheritance tree:

solo_founder (base: 2 agents)
  -> startup (extends solo_founder: adds CTO, PM, 2nd dev)
     -> dev_shop (extends startup: replaces devs with specialized roles, adds QA, DevOps)
     -> product_team (extends startup: adds design, data, QA)

research_lab (standalone)
  -> data_team (extends research_lab: data-focused subset)

agency (standalone -- too different to extend)
full_company (standalone -- comprehensive, not a progression)
consultancy (standalone)

Benefits

• Reduces YAML duplication across templates
• Validates the inheritance system with real usage (not just test fixtures)
• Shows users the natural scaling path
• Makes it easy for user-defined templates to extend builtins
• Child templates only define deltas (new agents, overrides, removals)

Considerations

• Base templates must be solid before building the tree (depends on v0.4.8 content improvements)
• Inheritance adds complexity for debugging -- each template must still be independently understandable
• merge_id must be set on all agents that children might target

Scope

Rewrite YAML files to use extends. Add merge_id to base template agents. Update tests to verify inheritance produces correct expanded configs.

Dependencies

• feat: differentiate template operational configs (autonomy, communication, workflow) #717 -- operational config differentiation (so base configs are correct before extending)
• feat: diversify personality preset assignments across templates #718 -- personality preset diversification (so presets are correct before extending)
• feat: add reporting lines, escalation paths, and workflow handoffs to templates #719 -- reporting lines (so structure is correct before extending)