Guide seat count confirmation before showing billing preview

[asizikov]

Summary

Organization usage CSVs can omit licensed users who had no billable activity during the report period, which can make the first billing preview less accurate. This PR adds a guided confirmation step so users can review seat counts before seeing the billing preview.

Changes

Commit	Change
refactor: share seat count helpers	Extracts reusable seat count normalization and validation helpers, with unit coverage for preserving historical minimum counts.
feat: review licensed seats before estimates	Adds an initial seat count confirmation step after organization reports are processed, applies confirmed seat counts to included AI Credits calculations, and links users back to adjust counts later.
fix: address seat count review feedback	Handles whitespace-only seat count input consistently and clears stale recalculation errors before retrying.

• Shows a "Review licensed seat counts" screen before the main report for organization-scoped uploads.
• Adds an Overview action to adjust seat counts from the Users section.

Testing

• npm run build
• npm run lint
• npm test

Checklist

• Specs lint passes (npm run lint)
• Tests updated if applicable
• Documentation updated if applicable

[Copilot]

Pull request overview

This PR adds a guided “Review licensed seat counts” step for organization-scoped uploads so users can confirm/adjust Copilot Business & Enterprise seat totals before seeing billing estimates, improving included AI Credits calculations when CSVs omit inactive licensed users.

Changes:

• Introduces shared seat-count parsing/normalization + validation helpers with unit tests.
• Adds a new SeatCountConfirmation screen gated to organization-scoped reports and wires confirmed counts into recalculation.
• Adds an Overview CTA to jump to the Users view to adjust seat counts later.

Show a summary per file

File	Description
src/App.tsx	Adds seat confirmation flow/state, applies confirmed seat overrides, and exposes “adjust seat counts” navigation.
src/components/SeatCountConfirmation.tsx	New UI screen to review/confirm licensed seat counts before showing estimates.
src/utils/seatCounts.ts	New shared helpers for seat normalization/parsing and reduction validation messaging.
src/utils/seatCounts.test.ts	Unit tests for the shared seat-count helpers.
src/views/UsersView.tsx	Refactors to use shared seat-count helpers when saving overrides.
src/views/OverviewView.tsx	Plumbs optional “adjust seat counts” callback into totals UI.
src/components/ui/BillingTotalsCards.tsx	Adds optional “adjust seat counts” action and updates explanatory copy.

Copilot's findings

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Comments suppressed due to low confidence (1)

src/utils/seatCounts.test.ts:16

• Consider adding a regression assertion that whitespace-only input does not trigger a reduction error (e.g. ' '), since Number(' ') becomes 0 and can otherwise incorrectly fail validation.

    expect(getSeatReductionError('', 10)).toBeNull()
    expect(getSeatReductionError('10', 10)).toBeNull()
    expect(getSeatReductionError('12', 10)).toBeNull()
    expect(getSeatReductionError('8', 10)).toBe('Cannot go below 10 because that count comes from historical report data.')

• Files reviewed: 7/7 changed files
• Comments generated: 4