Remove dead workflow modes from definitions.py and registry

[osilkin98]

Context

Of 21 registered workflow modes, only 4 core modes are needed: design, create, build (as library function for design), and spec-generate (invoked by design). The rest should be removed from the registry and their function definitions deleted from definitions.py (currently 4,565 lines).

Important: build_workflow() MUST be kept as a function — design_workflow() calls into it. Only its standalone --mode build registry entry and SKILL.md should be removed.

Modes to remove entirely (function + registry + SKILL.md)

Confirmed dead (0 git-log hits, no inheritance dependencies)

• founder_workflow() (99 lines)
• parallel_improve_workflow() (267 lines) — sole consumer of SubgraphForkNode/SelectionNode
• refine_workflow() (192 lines)
• deep_research_workflow()

Standalone wrappers for shared subgraphs

• study_standalone_workflow() (21 lines) — keep _study_subgraph() helper
• deep_qa_standalone_workflow() — keep _deep_qa_subgraph() helper

Non-core supported modes (user directive: only keep create + design)

• improve_workflow() (248 lines) — was base for research, but research is also being removed
• research_workflow(), research_standalone_workflow() — research-mode-only
• meta_workflow() — meta-mode-only (ACE evolution)
• discover_workflow() — keep factory discover as CLI command, remove standalone mode
• review_workflow() — eval-profile review gate
• doc_generate_workflow(), doc_update_workflow() — standalone documentation workflows
• spec_update_workflow() — standalone, not invoked by design
• evolve_workflow() — AlphaEvolve-style program evolution, NOT the outer loop

Frontend-design modes (0 git-log hits)

• frontend_design_workflow() (555 lines)
• frontend_design_scan_workflow() (170 lines)
• frontend_design_discover_workflow() (228 lines)
• Delete factory/agents/prompts/frontend_design/ subdirectory

What to keep

• design_workflow(), create_workflow(), spec_generate_workflow()
• build_workflow() as library function (remove registry entry + SKILL.md only)
• Shared subgraph helpers: _study_subgraph(), _deep_qa_subgraph(), _research_subgraph()
• All contributed benchmark workflows (not touching those)

Also remove

• Corresponding skills/workflow-*/SKILL.md files for deleted modes
• Run factory workflow export-skills after to regenerate remaining SKILL.md files

Related

• Supersedes Move non-core workflow modes out of definitions.py #1330 (move non-core modes — this goes further: delete them)
• Enables Prune unused node types: SubgraphForkNode, SelectionNode, LLMNode #1328 (prune unused node types)
• Dead-code pruning report — comprehensive analysis of ~7,800 removable lines #1301 (dead-code pruning report)