Feature enhancement — smarter incident banner targeting logic
## What is the current behavior?
Displaying the incident banner requires toggling a flag or environment
variable. Banners are shown to all users regardless of whether their
projects are in affected regions or whether the incident affects project
creation.
## What is the new behavior?
Banner visibility is now driven by `show_banner` metadata from the
StatusPage API — no manual flag or env var toggle needed. Per-user
targeting is then applied:
- Users with projects only see the banner when they have a database in
an affected region
- Users without projects only see the banner when the incident affects
project creation
Incident responses are enriched with cache data (`affected_regions`,
`affects_project_creation`) fetched from a Supabase table. Visibility
logic is extracted into a dedicated hook and pure utility function,
backed by unit tests.
## Additional context
Resolves FE-2562
Charis