fix(roi): repair $NaN / [object Object] in cco-roi cost table

[egorfedorov]

Summary

/cco-roi is fully broken in its money output — same bug class as #29, just in src/roi.js instead of src/report.js.

Bug

roi.js treats MODEL_COSTS[model] as a scalar price per million tokens:

const cost = MODEL_COSTS[model];          // line 58
const costPerSession = (avgTokens / 1e6) * cost;
pricePerM: `$${cost}`,

But in utils.js the values are objects:

'opus': { input: 5, output: 25, contextWindow: 1_000_000 },

So tokens * { input, output, ... } → NaN, and `$${cost}` → $[object Object]. The entire "Monthly Savings by Model" table and the "Team ROI" figures were garbage.

Before:

Model     $/M tok            Per session   Per day    Per month   Per year
Haiku     $[object Object]   $NaN          $NaN       $NaN        $NaN
...
Team ROI: Monthly: $NaN

Fix

Use the MODEL_INPUT_COST accessor utils.js already exports for exactly this (input price per model), matching the #29 fix.

After:

Model     $/M tok   Per session   Per day    Per month   Per year
Haiku     $1        $0.01         $0.05      $1          $17
Sonnet    $3        $0.03         $0.14      $4          $52
Opus      $5        $0.05         $0.24      $7          $86
Team ROI: Monthly: $70   Yearly: $840

Verification

• node --check src/roi.js → OK
• node src/roi.js → real numbers, no NaN / [object Object]
• npm test → 139/139 pass

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