fix: remove erroneous cents-to-dollars division in notification currency formatting

[devin-ai-integration]

Summary

Fixes incorrect order amounts displayed in notification email previews. A $149.99 order was rendering as $1.50 due to an erroneous division by 100 in the NotificationRenderer.FormatCurrency() method.

Root Cause

During the microservice decomposition, the NotificationRenderer.FormatCurrency() method was written with an incorrect assumption documented in a misleading comment:

// The OrderPlacedEvent.TotalAmount is transmitted in cents (integer
// representation) to avoid floating-point precision issues across
// service boundaries. Convert back to dollars for display.
var dollars = amount / 100m;

However, the OrderPlacedEvent contract in Shared.Contracts defines TotalAmount as a decimal representing dollars, not cents. The Order service sends 149.99 (dollars), but the renderer divides by 100, producing 1.4999 → rounded to $1.50.

Fix

Removed the /100m division — the amount is already in dollars and just needs formatting:

private static string FormatCurrency(decimal amount)
{
    return amount.ToString("C2");
}

Also fixed incorrect ProjectReference paths in Notification.API.csproj (../../Shared/ → ../../../Shared/) which prevented the project from building when referenced directly.

Before / After

Before (Bug)	After (Fix)

Review & Testing Checklist for Human

• Verify the Order service also transmits TotalAmount in dollars (not cents) when publishing OrderPlacedEvent via RabbitMQ in production — this fix assumes the HTTP testing endpoint matches the real contract
• Confirm no other services (e.g., shipping notifications) rely on the old cents-based interpretation

Notes

• The ¤ symbol in screenshots is the generic currency symbol used by .NET's ToString("C2") when running in invariant culture. In production with proper locale settings, this would display as $.
• The .csproj path fix (../../ → ../../../) was necessary to allow the Notification.API project to build standalone (resolves project reference to Shared.Contracts).

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/23895db2644343bca01a035cc250ced1
Requested by: @bsmitches

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[devin-ai-integration]

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[bsmitches]

Can you double check that this is the only place this bug exists? Also, please add inline comments around what you changed

[devin-ai-integration]

@bsmitches Searched the entire src/ tree for any similar / 100 or /100m patterns on monetary fields (amount, total, price, cost) — no other instances exist. The FormatCurrency method in NotificationRenderer.cs was the only place this bug occurred.

I've also pushed a follow-up commit (fc0f935) adding an inline XML doc comment on FormatCurrency clarifying that the amount is expected in the base currency unit (dollars), matching the OrderPlacedEvent contract.