feat: expand scenario dataset (target 20-50 scenarios)

[zenprocess]

Priority: High

3 scenarios won't give statistically significant results. Need breadth.

Proposed Scenario Categories

Category	Examples	Count
REST API (Python)	CRUD, auth, pagination, websockets	5
REST API (Go)	Chi router, middleware, gRPC gateway	3
CLI tools	argparse, file processing, data pipelines	3
React/frontend	Components, state management, forms	4
Full-stack	Frontend + backend + database	3
Refactoring	Split monolith, extract modules	3
Bug fixing	Given broken code, fix the bug	5
Test writing	Given code, write comprehensive tests	3

Contribution Model

Community contributions via the scenario request issue template.
Each scenario needs: 2+ agents, 3+ turns, tool calls, expect blocks, at least one steering/nudge variant.