[Reimbursements] Show banners when orgs have insufficient funds

[manuthecoder]

closes #13426

This pull request introduces a balance validation warning on the reimbursement report page

Added validation to alert users when a reimbursement exceeds available event funds:

• Implemented exceeds_event_balance? method in Reimbursement::Report to check if the requested amount surpasses the event's available USD balance for submitted reports
• Updated the report view to display an informational callout when the balance is exceeded on open reports, notifying users that additional funding may be required

[Copilot]

Pull request overview

Adds a “low/insufficient funds” warning to reimbursement report pages so users are informed when a submitted reimbursement amount exceeds the event’s available USD balance.

Changes:

• Introduces Reimbursement::Report#exceeds_event_balance? to detect when the report amount is beyond the event’s available USD balance.
• Updates the reimbursement report show view to render a warning callout for open reports that exceed available balance.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
app/models/reimbursement/report.rb	Adds a helper method to check whether a submitted report exceeds the event’s available USD balance.
app/views/reimbursement/reports/show.html.erb	Renders a warning callout intended to display when the report exceeds the event balance and is still open.

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[YodaLightsabr]

We currently already have a system in place for alerting users of insufficient funds:

hcb/app/views/reimbursement/reports/_actions.html.erb

Line 175 in 86da14e

<span class="bold warning">Warning</span>: your report is beyond your balance. To continue, lower the amount requested.

It looks like the only difference between the existing logic and this PR's logic is that this PR shows the warning even when a report requires peer review. If this difference is intentional, we should update the existing callout rather than creating a new one.