perf: restore SSR plugin catalog loading

[vyctorbrzezowski]

Summary

• restore the proposed /plugins/ catalog request to the real TanStack route loader after Show unfiltered browse totals #2586 moved it behind hydration
• key loader invalidation to request-affecting search state, while keeping view changes and search-only client sorting out of the cache key
• forward navigation cancellation and cap catalog loading at five seconds so a stalled backend cannot block SSR indefinitely
• keep this public browse surface explicitly anonymous so request-scoped private package visibility is never serialized into HTML or mixed into pagination
• anchor load-more state to the active loader result, abort stale pagination, and skip the redundant public-count subscription when loader data already has the total

This closes the confirmed /plugins/ loader item from #2925. The broader SSR auth, skill README, and Markdown rendering work remain explicitly out of scope.

Validation

• bunx vitest run src/__tests__/packages-route.test.tsx src/lib/packageApi.test.ts (100 passed)
• red/green regressions: effective search loader deps and stale pagination both fail against the previous implementation and pass in this PR
• bun run ci:static
• bun run ci:unit (4,605 passed, 1 skipped; coverage 85.59% statements / 75.35% branches / 86.79% functions / 88.51% lines)
• bun run ci:types-build
• git diff --check
• real browser proof at http://localhost:3000/plugins with the seeded local public corpus: SSR HTML contained all 3 fixture plugins; warm local TTFB was 0.28s; Chromium observed 0 catalog requests after hydration, 1 request for a category navigation, and 0 requests for a list/grid-only navigation

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[vyctorbrzezowski]

@clawsweeper review

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[vyctorbrzezowski]

ClawHub UI Proof

Status: passed
Mode: feature
Scenario: Rendered plugin catalog reference; SSR request measurements remain in the PR body
Provider: real Chromium against public ClawHub
Baseline: not run for feature proof.
Candidate: merged PR #3062 visual reference

Public plugin catalog rendered with live catalog data

Raw proof files: https://github.com/openclaw/clawhub/tree/qa-artifacts/clawhub-ui-proof/pr-3062/ssr-plugin-catalog-reference