Build the over-limit and restricted states for the usage page

[talissoncosta]

Goal. Build the states shown when an organisation goes past its plan limit, so it can see what happened, what it means and what restores normal service.

Problem. Neither state exists. The restricted one is unreachable anyway: a restricted organisation is sent to the blocked screen on every route except the organisations list, so the page that would explain it is the one page they cannot open.

Scope

• paid, over limit: the banner, and the line under the meter saying how far over they are
• free, over limit: that they have 7 days to bring usage down before serving pauses
• free, restricted: what is paused, what restores it, and the upgrade path
• usage, limit and the over-limit figures readable in every state
• allow the usage route while the organisation is blocked from admin, otherwise the restricted state cannot be reached

Correction: the 7 days is consumable. OrganisationBreachedGracePeriod is written on the first restriction and never deleted, and restrict_use_due_to_api_limit_grace_period_over drops the wait once it exists, so a repeat breach is restricted on the next task run. The notification emails already conditionalise on this. The API does not say which case an organisation is in, so the page cannot promise the deadline truthfully.

Status

#8432 ships the route fix and both over-limit states, and a restricted organisation now gets its own copy telling it what restores access. Still open:

• what is paused. stop_serving_flags is on the model but on no serializer, so the page can say an organisation is restricted but not whether flag serving stopped or only admin access. Requested on Return grace period state from the API #8256
• the 7 day warning for a first free breach. Needs the API to distinguish a first breach from a repeat, also Return grace period state from the API #8256
• a regression test for the route exception. Needs an e2e test that can set organisation-level flags; nothing in the Playwright suite does that today

Not here

• whether a paid customer is covered by grace or being charged. That is Display the grace period state on the dashboard #8264, which needs Return grace period state from the API #8256
• estimated overage cost. The page can say whether they are charged, not how much
• notification configuration

Done when

• a paid organisation over its limit sees the over-limit state
• a free organisation over its limit is told it has 7 days to act
• a restricted organisation loads the usage page and sees the restricted state
• every other route still blocks as it does today, and an unrestricted organisation sees no change