Closes#3460.
Renamed for accuracy — the page/nav item is the hive roster, not a
general dashboard overview. Nav label, page title, component name,
and file all renamed together so the internal name doesn't drift from
what's displayed (a component still called OverviewPage under a
'hives' nav label would be exactly the kind of stale prior-art that
makes the next contributor search harder, not less).
Closes#3410.
`ApiErrorPanel` renders a ProblemDetails (RFC 9457) error nicely, with a
copy button so the full text can be pasted straight into a bug report.
No truncation of `detail` — on the #3363 incident that motivated this
issue, that string was the entire diagnosis.
`readApiError`/`problemMessage`/`ProblemDetails` are promoted out of
credentials.js's original `readErrorBody` into `@hive/shared/api-error.js`
(comment rewritten: the RFC 9457 rework has already landed everywhere
except swarm-controller's status route, #3412 in flight, so the raw-text
fallback is a compat shim for that one gap, not a general transition).
credentials.js's 4 call sites switch to the shared reader (kept as
one-line messages there, its result slots are single-line aria-live
regions, not a panel context).
Wired ApiErrorPanel into OverviewPage.tsx (the issue's own worked
example) and CreateAgentPage.tsx (second real call site).
Not built on <hive-warn> despite matching its visual language — that
custom element's CSS-as-text import only works under a build with
loader: 'text' for .css (dashboard's), and silently renders unstyled
under swarm-ui's default css loader (filed separately as #3415).
ApiErrorPanel is a self-contained light-DOM component instead, per
mara's own suggestion to keep it independent of the old UI's shapes.
Per mara's review on PR#3342 — the hive-status view shouldn't live
inline in App.tsx. Moves it to pages/OverviewPage.tsx, mirroring
JobsPage's shape: App.tsx stays routing-only, each page owns its own
fetch + render.
