feat(requests): paginate the request list

[Fluory]

Ziel

The request list (/requests, #26 / PR #43) stays fast and readable with thousands of requests per company. Today it loads every matching request at once.

Akzeptanzkriterien

• The list shows a fixed page size (e.g. 50) with next/previous navigation; filters (status, possible duplicate) survive paging.
• Paging is stable while new requests arrive (keyset on created_at, id, not OFFSET).
• Page parameters from the query string are validated (allow-list / bounds); invalid values fall back to the first page.
• Export records and retry info are loaded only for the requests on the current page (no N+1, no full scan).
• Tenant isolation unchanged: only the session's company, via withTenant.

Nicht Teil dieser Aufgabe

• Full-text search, sorting by other columns.

Betroffene Bereiche

• src/features/requests/repository.ts (listRequests), src/features/export/repository.ts (listExportRecords), src/app/requests/page.tsx

Testplan

Kriterium	Prüfart
Page size + navigation + filters	integration test
Stable keyset paging with inserts between pages	integration test
Invalid page params	unit test
Other company's requests never appear	integration test (two tenants)

Offene Entscheidungen

• Page size; whether a total count is needed (costs a COUNT per page view).

Security/Privacy betroffen?

Nein (query parameters validated; tenant isolation unchanged).

Found in the review of PR #43.

[Fluory]

Claimed by @Fluory (Claude Code session) on branch claude/feat-request-pagination-48. It is stacked on PR #53, because both change the request list page. Draft PR follows.

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