Global "degraded" incident banner shows a different subnet's status than the one you're viewing, with no clarifying context

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Context

Confirmed via direct interactive testing: navigating to a subnet's detail page (e.g. SN1 / Apex) shows a persistent top banner reading "DEGRADED · dead · SN10" — SN10's incident, not SN1's — with no text distinguishing "this is a network-wide notice, unrelated to the subnet you're currently viewing." A user skimming the page could easily misread this as the current subnet's own health status, since it renders directly above the subnet's own masthead with no visual or textual separation establishing it's global/unrelated.

Requirement

The global incident banner must make clear it's reporting a network-wide (or otherwise unrelated-to-the-current-page) incident, not the status of the page the user is currently viewing — whenever the incident it's reporting concerns a different entity than the current page's subject.

Deliverable

• File to check/fix: the site-wide incident-banner component (likely apps/ui/src/components/metagraphed/incident-strip.tsx or similar — confirm exact location) and wherever it's mounted relative to subnets.$netuid.tsx's masthead.
• What "done" looks like concretely: when the banner's incident subject differs from the current route's subject (e.g. banner is about SN10, current page is SN1), the banner text should make the distinction explicit — e.g. "Degraded: SN10 (Swap) — unrelated to this page" or similar, or the banner could conditionally suppress/de-emphasize itself on subnet-detail pages for a different subnet's incident and instead surface it in a more clearly-global location (e.g. only on Home/Status/Explorer). Exact approach is a design call — the core requirement is: no ambiguity about which subnet a displayed incident concerns.

Acceptance criteria

• The incident-banner component appears in the diff
• When viewing a subnet detail page for subnet A while subnet B has an active incident, the banner text (or its absence/relocation) makes unambiguous that the incident concerns subnet B, not A
• When viewing the subnet that actually has the incident, the banner continues to read naturally as being about "this" subnet
• Includes a before/after screenshot showing the banner on an unrelated subnet's page, both themes, per the repo's UI-PR requirement

Non-goals

• Don't change how incidents are detected/computed — this is a display-clarity fix for an existing, otherwise-correct signal.
• Don't remove the global banner entirely — network-wide incident visibility is valuable, it just needs to be unambiguous about scope.

Size

Size: S — keep this PR small (aim for ≤10 files / ≤1000 LOC).

Part of #2542.

[linear-code]

JSO-2891