[AOE] Reservation workbooks show absolute quantities on the wrong ratio scale

Problem

The reservation workbooks convert quantities into "smallest SKU" units by multiplying with the ISF Ratio:

| extend AvgRIsUsedInSmallestRatio = Ratio * AvgRIsUsedDaily
| summarize TotalReservedQuantity_s = sum(todouble(TotalReservedQuantity_s) * Ratio), ... by ISFGroup

That conversion only holds if the smallest SKU in a group has ratio 1. Since #2222 the workbooks read src/open-data/InstanceSizeFlexibility.csv, which comes from the Catalogs API and is not normalized — Microsoft's own ISF documentation states it plainly:

The raw ISF ratios from the API and powershell don't always start at 1 for the smallest SKU in a group. For example, the BS Series group starts at 0.25 and the Ddsv5 Series starts at 2.

Measured on the published dataset: 162 of 319 groups start at 1, 157 do not. The retired isfratioblob.csv the workbooks read before #2222 was normalized (432 of 433 groups started at 1).

Impact

Utilization percentages are correct. UsedQuantity / TotalReservedQuantity * 100 carries the factor on both sides, so it cancels.

Absolute quantities are wrong by each group's constant factor. AvgRIsUsedDaily derives from Quantity * RINormalizationRatio, so it is already in reservation units of the purchased SKU; multiplying by a non-normalized Ratio does not land in smallest-SKU units, which is what the column name claims and what the displayed TotalReservedQuantity implies.

Fix

Normalize inside the workbook queries — divide each group's ratios by that group's minimum:

let ISFGroups = externaldata(ISFGroup:string, ArmSKUName:string, Ratio:double)
    [@"https://raw.githubusercontent.com/microsoft/finops-toolkit/dev/src/open-data/InstanceSizeFlexibility.csv"]
    with(ignoreFirstRecord=true)
| extend ArmSKUName = tolower(ArmSKUName)
| summarize MinRatio = min(Ratio) by ISFGroup
| join kind=inner (...) on ISFGroup
| extend Ratio = Ratio / MinRatio;

Contained to AOE, leaves the open data and the Power BI models untouched.

Affected files, all reading the same CSV via externaldata():

• src/optimization-engine/views/workbooks/reservations-usage.json
• src/optimization-engine/views/workbooks/reservations-potential.json
• src/optimization-engine/views/workbooks/benefits-simulation.json

Alternative

Publish the open data normalized instead, which would restore parity with the retired file for every consumer at once. That is a larger decision: it changes published values in 156 of 318 groups. It would not affect the Power BI models, which use the flexibility group but never the ratio.

Not a regression from #2300

Pre-existing since #2222 migrated the workbooks off the retired blobs. #2300 changed no published ratio — it only added rows.