Add ACH-enhanced deep research, upgrade research workflow

[5uck1ess]

Summary

• Upgraded research skill — query decomposition with explicit goals, iterative summarization, source corroboration tracking (CONFIRMED/UNCORROBORATED/CONTESTED)
• New deep-research skill + command — Analysis of Competing Hypotheses (ACH) pipeline: perspective discovery, directed disconfirmation, evidence matrix, sensitivity analysis, self-critique
• New deep-research.yml workflow — 13-step YAML workflow for the Go engine
• Updated research.yml workflow — matches upgraded skill with decomposition and corroboration steps

Design

Two tiers triggered by keyword:

• "research X" → lightweight search/synthesize (~200k budget)
• "deep research X" → full ACH pipeline (~400k budget)

ACH pipeline (from CIA methodology):

1. Discover perspectives from overview articles
2. Decompose into sub-questions with disconfirmation queries
3. Extract atomic claims from sources
4. Generate 2-4 competing hypotheses
5. Directed disconfirmation — try to KILL each hypothesis
6. Evidence matrix — score by fewest inconsistencies
7. Sensitivity check — identify linchpin evidence
8. Self-critique before output

Test plan

• Run /devkit:deep-research on a real question and verify full ACH pipeline executes
• Run research skill on a simple question and verify it stays lightweight
• Verify YAML workflows parse correctly via devkit workflow deep-research
• Check README/ROADMAP counts are accurate (21 commands, 16 skills, 13 workflows)