Add ROI framework and three-year NPV worksheet for enterprise Claude seat purchases

[malston]

Summary

Adds two companion articles to the enterprise rollout binder, both in 00-overview/, for a company weighing a per-seat Claude Enterprise purchase as a broad enterprise AI investment:

1. ROI Framework (roi-framework.md, weight 3) -- the single-year decision model.
2. Three-Year NPV Worksheet (three-year-npv-worksheet.md, weight 4) -- the multi-year discounted view, in the fill-in style of context-budget-worksheet.md.

The worksheet carries the framework's illustrative figures across three years (adoption ramp + end-of-year discounting) so the two pages reconcile.

ROI Framework covers

• The equation, with the two honesty levers (value-conversion factor, active-seat ratio) up front.
• Cost (TCO): subscription, integration, enablement, admin, adoption drag; NPV for the multi-year view.
• Benefit: category-to-measurement table anchored on DORA/SPACE for engineering and time-and-task studies elsewhere.
• Value-conversion factor, Forrester TEI risk adjustment, adoption weighting.
• A worked example, baseline-before-you-buy, and a "where the number lies" list.

NPV Worksheet covers

• The discount mechanic and convention (end-of-year, Year-0 setup at DF 1.0).
• Inputs table, year-by-year build, headline results (NPV, ROI, payback, IRR).
• Sensitivity table plus a break-even benefit multiplier (~42% of plan) as the margin-of-safety headline.
• Fill-in steps.

Notes for review

• No asserted pricing. Claude Enterprise seat pricing is negotiated (contact-sales); the models run on variables and all dollar figures are labeled illustrative.
• Verify before customer use: Forrester TEI bucket naming / the commissioned Claude study, and the DORA/SPACE attributions, against authoritative sources.
• Follows STYLE-GUIDE.md; hugo --gc --minify builds clean (105 pages).
• Internal links use the binder's relative-path convention.

[Copilot]

Pull request overview

Adds a new enterprise-rollout binder article that provides a fill-in ROI/payback model for per-seat Claude Enterprise purchases, intended to sit immediately after the Executive Summary and serve as the shared financial “math layer” for related pages.

Changes:

• Introduces an ROI + payback equation with explicit “honesty levers” (value-conversion factor, active-seat ratio).
• Defines a TCO breakdown and benefit measurement categories (with DORA/SPACE and time-and-task study guidance).
• Includes a worked example, baseline guidance, and a checklist of common modeling failure modes.

[malston]

Fixed in 5708641. Confirmed the diagnosis: per-active-user benefit ($3,240) x (active/purchased = 0.7) = $2,268, i.e. benefit per purchased seat, not the total the label implied. Rather than relabel to per-purchased-seat units, restated it as total benefit so it matches how the rest of the model (worked example, NPV worksheet) uses benefit:

Total benefit = per-active-user benefit x active seats
              = per-active-user benefit x purchased seats x active-seat ratio

This reconciles numerically ($3,240 x 500 x 0.7 = $1,134,000, matching the worked example) and makes the active-seat-ratio scaling the section is about explicit.