feat(nexus-operations): add loading state to standalone nexus operations list page header

[rossedfort]

Description & motivation 💭

The standalone nexus operations list page header showed "0 Nexus Operations" and empty/missing status badges during the initial API fetch. This happened because the header rendered immediately from store defaults (count=0) while the table's internal pagination store was still loading.

This PR surfaces the table's internal loading state up to the page header via a new optional onLoadingChange callback on api-paginated.svelte, then uses it to drive improved loading UX in the header:

• Count/timestamp: Instead of swapping to skeleton bars and back (which caused layout shift), the header now keeps the previous count visible at all times. On first load this shows "0 Nexus Operations" only briefly before the real count arrives — the same behaviour as the workflows list page.
• Status count badges: StatusCounts and CountRefreshButton are now always mounted (matching the workflows page pattern). StatusCounts already has its own internal per-badge skeleton loader and a min-h-[24px] wrapper, so badges animate in without resizing the header.

Changes:

• api-paginated.svelte: add optional onLoadingChange?: (loading: boolean) => void prop (with `$$Props` type update) and a reactive statement to fire it
• nexus-operations-summary-configurable-table.svelte: wire nexusOperationLoading store via the new callback
• standalone-nexus-operations.svelte: remove loading guards; always render h1, timestamp, CountRefreshButton, and StatusCounts

Screenshots (if applicable) 📸

Screen.Recording.2026-07-08.at.11.31.16.AM.mov

Design Considerations 🎨

Follows the established pattern in workflows-with-new-search.svelte, which renders StatusCounts and CountRefreshButton unconditionally. StatusCounts self-manages its badge skeleton state internally.

Testing 🧪

How was this tested 👻

• Manual testing
• E2E tests added
• Unit tests added

Steps for others to test: 🚶🏽‍♂️🚶🏽‍♀️

1. Navigate to a namespace's standalone Nexus Operations list page
2. Hard-refresh — the header shows the previous count without layout shift while the table loads
3. Status badges animate in via internal skeleton loaders rather than appearing abruptly after a blank gap
4. Trigger a manual refresh via CountRefreshButton — same stable layout during reload

Checklists

Draft Checklist

Merge Checklist

Issue(s) closed

DT-4239

Docs

Any docs updates needed?

No docs changes needed.

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Project	Deployment	Actions	Updated (UTC)
holocene	Ready	Preview, Comment	Jul 8, 2026 5:36pm

[temporal-cicd]

Warnings

⚠️

📊 Strict Mode: 2 errors in 1 file (0.2% of 858 total) src/lib/holocene/table/paginated-table/api-paginated.svelte (2) L104:20: Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ items: T[]; nextPageToken: string; }'. L120:20: Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ items: T[]; nextPageToken: string; }'.

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