Show a "source unavailable" notice instead of "0 in view" in the mobility panel #412

Problem

When the OpenConditions fuel, charging or parking source isn't ready, the provider returns partial: "unavailable" (e.g. integrations/openconditions/fuel/provider.ts). apps/web/src/components/panels/datasource/DataSourceFilterContent.tsx only renders a notice for partial === "area". So an unavailable source with no results reads "0 in view", which implies there are no stations here.

Deliverable

• A localized notice for partial === "unavailable", with retry guidance and no "zoom in" action. Usable partial results stay visible.
• Provider, viewport and filter changes clear a stale notice.
• Panel tests that tell unavailable, empty and area-limited apart.
• Phone and desktop screenshots in light and dark mode in the PR.

Out of scope

Separate issues, only if needed: basemap-bounds notices, a public coverage contract, freshness thresholds and per-country documentation.