feat: add progressive-estimation skill for AI-assisted development estimation (#260)

Co-authored-by: Stas <stas@mac-1.home>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

skills/progressive-estimation/SKILL.md

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+---
+name: progressive-estimation
+description: "Estimate AI-assisted and hybrid human+agent development work with research-backed PERT statistics and calibration feedback loops"
+category: project-management
+risk: safe
+source: community
+date_added: "2026-03-10"
+author: Enreign
+tags:
+  - estimation
+  - project-management
+  - pert
+  - sprint-planning
+  - ai-agents
+tools:
+  - claude
+---
+
+# Progressive Estimation
+
+Estimate AI-assisted and hybrid human+agent development work using research-backed formulas with PERT statistics, confidence bands, and calibration feedback loops.
+
+## Overview
+
+Progressive Estimation adapts to your team's working mode — human-only, hybrid, or agent-first — applying the right velocity model and multipliers for each. It produces statistical estimates rather than gut feelings.
+
+## When to Use This Skill
+
+- Estimating development tasks where AI agents handle part of the work
+- Sprint planning with hybrid human+agent teams
+- Batch sizing a backlog (handles 5 or 500 issues)
+- Staffing and capacity planning with agent multipliers
+- Release date forecasting with confidence intervals
+
+## How It Works
+
+1. **Mode Detection** — Determines if the team works human-only, hybrid, or agent-first
+2. **Task Classification** — Categorizes by size (XS–XL), complexity, and risk
+3. **Formula Application** — Applies research-backed multipliers grounded in empirical studies
+4. **PERT Calculation** — Produces expected values using three-point estimation
+5. **Confidence Bands** — Generates P50, P75, P90 intervals
+6. **Output Formatting** — Formats for Linear, JIRA, ClickUp, GitHub Issues, Monday, or GitLab
+7. **Calibration** — Feeds back actuals to improve future estimates
+
+## Examples
+
+**Single task:**
+> "Estimate building a REST API with authentication using Claude Code"
+
+**Batch mode:**
+> "Estimate these 12 JIRA tickets for our next sprint"
+
+**With context:**
+> "We have 3 developers using AI agents for ~60% of implementation. Estimate this feature."
+
+## Best Practices
+
+- Start with a single task to calibrate before moving to batch mode
+- Feed back actual completion times to improve the calibration system
+- Use "instant mode" for quick T-shirt sizing without full PERT analysis
+- Be explicit about team composition and agent usage percentage
+
+## Common Pitfalls
+
+- **Problem:** Overconfident estimates
+  **Solution:** Use P75 or P90 for commitments, not P50
+
+- **Problem:** Missing context
+  **Solution:** The skill asks clarifying questions — provide team size and agent usage
+
+- **Problem:** Stale calibration
+  **Solution:** Re-calibrate when team composition or tooling changes significantly
+
+## Related Skills
+
+- `@sprint-planning` - Sprint planning and backlog management
+- `@project-management` - General project management workflows
+- `@capacity-planning` - Team velocity and capacity planning
+
+## Additional Resources
+
+- [Source Repository](https://github.com/Enreign/progressive-estimation)
+- [Installation Guide](https://github.com/Enreign/progressive-estimation/blob/main/INSTALLATION.md)
+- [Research References](https://github.com/Enreign/progressive-estimation/tree/main/references)