feat(ui): add shared analytics-card skeleton + empty-state shell (#2200)

[dhgoal]

Adds a shared analytics-card skeleton + empty-state treatment (Closes #2200).

New AnalyticsCardShell (apps/gittensory-ui/src/components/site/app-panels/analytics-card-shell.tsx): a titled analytics card that renders one of three states — a skeleton shimmer while the metric loads, an EmptyState with a hint when it has no data, or its ready content — so the new analytics cards share one loading/empty look instead of each re-inventing it. Presentational only; the caller decides the state from its own data.

Adoption: the analytics route's cycle-time slot now renders the shared empty card (with a hint) when its data is absent, instead of rendering nothing.

UI Evidence

Rendered with the app's compiled stylesheet; .dark theme toggled on the document. Desktop (1440) and mobile (390) at 2× DPR.

State	Light	Dark
Ready — desktop
Empty — desktop
Loading (skeleton) — desktop
Ready — mobile
Empty — mobile

Test

analytics-card-shell.test.tsx — ready (title + description + content), empty (title + hint, no ready content), loading (skeletons, no ready content), and no-description. 4 tests pass. ui:typecheck + ui:build green; new files prettier + eslint clean.

• Conventional Commit; Closes feat(ui): shared analytics-card empty + loading skeleton states #2200. No site//CNAME/**/lovable/**; no CHANGELOG.md. UI Evidence attached (GitHub-hosted PNG thumbnails); no review-only screenshots committed to the repo.

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✅ Gittensory review result - approve/merge recommended

_{Review updated: 2026-07-10 20:34:24 UTC}

3 files · 1 AI reviewer · no blockers · readiness 100/100 · CI green · unstable

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
Adds a shared AnalyticsCardShell component (loading/empty/ready states) and adopts it for the cycle-time card's empty state in app.analytics.tsx, replacing a prior null-render with a titled empty-state card plus hint text. The component is simple, purely presentational, and is exercised by tests for all three states plus the no-description case; the only behavioral change is narrowly scoped to the cycle-time slot exactly as described. No correctness, security, schema, or migration issues are visible in the diff.

Nits — 5 non-blocking

• The PR description frames this as a shell for 'every analytics card' but only the cycle-time slot in app.analytics.tsx:187-196 actually adopts it — worth confirming whether wider adoption (gate-precision, usage panels) is planned as a follow-up or intentionally out of scope for feat(ui): shared analytics-card empty + loading skeleton states #2200.
• EmptyState's description prop behavior isn't visible in this diff — confirm it renders both plain strings and ReactNode consistently with the emptyHint usage here.
• The loading skeleton in analytics-card-shell.tsx always renders exactly 3 placeholders regardless of the eventual ready-content shape; fine today but could use a column-count prop if adopted by a card with a different layout.
• Consider parameterizing the skeleton column count (default 3) before adopting this shell more broadly.
• External brief flags 'feat(ui): shared analytics-card empty + loading skeleton states #2200 coverage: partial' — worth double-checking the linked issue's scope matches exactly this single-card adoption before merge.

Flagged checks (non-blocking)

• Contributor trust — Contributor flagged for review

Signal	Result	Evidence
Code review	✅ No blockers	1 reviewer
Linked issue	✅ Linked	#2200
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 94 registered-repo PR(s), 53 merged, 7 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	dhgoal; Gittensor profile; 94 PR(s), 7 issue(s).
Gate result	✅ Passing	No configured blocker found.

Review context

• Author: dhgoal
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: not available
• Official Gittensor activity: 94 PR(s), 7 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Keep the PR focused and include validation evidence before maintainer review.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

Visual preview

Route	Viewport	Before (production)	After (this PR's preview)	Diff
/app/analytics	desktop			—
/app/analytics	mobile			—

Click any thumbnail to open the full-size screenshot. Before = production · After = this PR's preview deploy.

_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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Gittensory approves — the gate is satisfied and CI is green.