feat(wave): cursor pagination for the issues list (#635)

[efstajas]

Summary

Migrates the Wave issues list to keyset/cursor pagination, paging the infinite scroll via the backend's pagination.nextCursor instead of incrementing page.

Deep page-based scrolling drove the slow OFFSET query path on GET /api/issues that pinned DB pool connections and caused production 5xx incidents (drips-network/wave#635). Cursor pagination is O(limit) regardless of depth.

Depends on the backend PR drips-network/wave#637 (which adds pagination.nextCursor and ?cursor=).

What changed

• types/pagination.ts: optional cursor input param + nextCursor response field (string | null).
• toPaginationParams emits the cursor query param.
• issues-page.svelte getMoreIssues: prefers pagination.nextCursor; falls back to page + 1 for sorts the backend doesn't cursor-paginate (points) and for older backends that don't return nextCursor.

Backwards compatibility

Fully backwards-compatible and safe to deploy in either order relative to the backend: when no nextCursor is returned (old backend, or points sort) it transparently uses page-based loading. The infinite-scroll terminator (hasNextPage) and match-count badge (total) are unchanged — both are still returned by the backend in cursor mode.

Testing

• New types/pagination.unit.test.ts: toPaginationParams cursor serialization/encoding; paginationSchema accepts string/null/absent nextCursor.
• npm run test:unit → 93 passed.
• npm run check → 0 errors. eslint/prettier clean on changed files.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Migrates Wave issue infinite scrolling toward cursor/keyset pagination while keeping offset pagination as a fallback for unsupported sorts or older backends.

Changes:

• Adds optional nextCursor parsing and cursor query serialization to shared pagination utilities.
• Updates the issues page infinite-scroll loader to prefer pagination.nextCursor before falling back to page + 1.
• Adds unit coverage for cursor serialization and nextCursor schema handling.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/lib/utils/wave/types/pagination.ts	Extends pagination schema/input utilities for cursor support.
src/lib/utils/wave/types/pagination.unit.test.ts	Verifies cursor query params and optional/null nextCursor parsing.
src/lib/components/wave/issues-page/issues-page.svelte	Uses cursor-based loading for subsequent issue pages when available.

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