fix(events): use terse route availability copy

[harshtandiya]

What changed

The event URL field said availability in full sentences, one per reason. EventRoute.vue
already renders the message beside a check / triangle-alert icon in green or red, so the
icon and colour carry the verdict — the text only needs the status word (per #434).

Two states now, not four. A reserved route and a blank one read the same as a claimed
one: the organiser types a different route either way, so why it is unavailable is noise.

case	before	after
free	This route is available.	Available
taken	This route is already taken.	Already exists
reserved	'{0}' is reserved and cannot be used.	Already exists
blank	Enter a route.	Already exists

Backend-only (route_availability in buzz/api/events/services.py); strings stay in _()
and RouteAvailability's shape is unchanged.

Closes #434

Demo

free	taken	reserved

The blank case has no shot: the component clears the message on an empty field, so it
never reaches the screen. The branch is kept for API callers.

Testing

• bench run-tests --module buzz.api.events.test_events — 80 passed. The route tests
  assert on .available, which did not change.
• Screenshots above taken against a local bench on this branch.
• e2e/tests/manage-event.spec.ts had three assertions on the old copy; all retargeted.
  Not run locally — left to CI.

[greptile-apps]

Greptile Summary

The PR simplifies event-route availability messages while preserving availability decisions and response structure.

• Consolidates blank, reserved, and claimed routes under “Already exists.”
• Replaces the successful availability sentence with “Available.”
• Updates end-to-end assertions for the new exact copy.

Confidence Score: 5/5

The PR appears safe to merge because it preserves route-availability behavior and updates the affected end-to-end expectations consistently.

No actionable failures remain; short-circuit evaluation retains the prior blank and reserved-route behavior, and the UI tests reliably match the new rendered messages.

Important Files Changed

Filename	Overview
buzz/api/events/services.py	Consolidates unavailable-route handling and shortens translated availability messages without changing boolean semantics.
e2e/tests/manage-event.spec.ts	Updates route-availability assertions to verify the new exact copy for free, claimed, and reserved routes.

_{Reviews (1): Last reviewed commit: "Merge branch 'develop' into fix/434-rout..." | Re-trigger Greptile}