feat: add /cfo skill — technology cost analysis and ROI

[HMAKT99]

"What does our technology actually cost per user?"

The board asks every quarter. Engineering guesses. Nobody knows the real infrastructure cost per user, which services scale linearly vs exponentially, or that the abandoned Redis cache is still costing $200/month.

What /cfo does

You:   /cfo

Claude: INFRASTRUCTURE COST MODEL
        Service          Cost Driver        Est. Monthly    Scaling
        Database         Storage + IOPS     ~$400/mo        Linear
        Redis            Memory             ~$80/mo         Linear
        CI/CD            Build minutes      ~$150/mo        Linear w/ PRs
        Monitoring       Per-host           ~$200/mo        Step function ←

        TECHNICAL DEBT BALANCE SHEET
        Category          Items   Est. Hours   Interest Rate
        Missing tests      12      ~40 hrs      Medium
        Deprecated deps     8      ~20 hrs      High (security)
        Manual processes    3      ~6 hrs/mo    Continuous ←

        TOTAL PRINCIPAL:    ~80 engineering hours (~$12,000)
        MONTHLY INTEREST:   ~6 hrs/month in friction

        BUILD vs. BUY:
        Auth (Auth0)     $300/mo   ~8 eng-weeks to build   → BUY
        Search (Algolia) $500/mo   ~3 eng-weeks to build   → EVALUATE

Maps services to cost drivers. Quantifies tech debt as a balance sheet. Build-vs-buy scorecards. Scaling projections at 10x/100x. Engineering ROI from git history.

Only .tmpl committed — bun run gen:skill-docs generates the rest.

Test plan

• .tmpl follows template pipeline
• Registered in gen-skill-docs.ts, skill-check.ts, test files