Add body-size limit middleware shim for routes-b

[Johnpii1]

close #554

Description
Added helper libraries under app/api/routes-b/_lib: ageing.ts (UTC day calc + bucket logic), invoice-archive.ts (include flag + filter), invoice-filters.ts (filter parsing/validation), and with-body-limit.ts (1 MiB default body-size wrapper with streaming fallback).
Extended GET /api/routes-b/invoices/overdue with ?bucketed=true to return { buckets: { 1_30, 31_60, 61_90, 90_plus }, totals } while preserving the original flat response when bucketed is absent, using UTC-based days-overdue computation.
Added archive endpoints POST /api/routes-b/invoices/[id]/archive and POST /api/routes-b/invoices/[id]/unarchive, an GET /api/routes-b/invoices/archived list, and wired ?includeArchived=true (default lists exclude archived) into invoices listing routes, implemented via the new archive helper.
Implemented multi-field filters in GET /api/routes-b/invoices (number, client, minAmount, maxAmount, currency) with validation and AND semantics using the new filter builder.
Introduced withBodyLimit and applied it to starter routes inside routes-b (branding, contacts PATCH, tags POST, webhooks POST, reminder-settings PATCH) and provided a per-route override example for avatar PATCH (2 MiB).
Added unit tests under app/api/routes-b/tests for ageing bucket boundaries and response shape, archive/unarchive behavior and default exclusion, invoice filter behavior and invalid amounts, and body-size limit scenarios.

Testing
Unit tests were added covering ageing boundaries and bucket shape, archive/unarchive and list include/exclude, invoice filter application and invalid amounts, and body-size wrapper behavior (files: app/api/routes-b/tests/.test.ts).
Attempted to run the test suite via npx vitest run app/api/routes-b/tests/.test.ts, but test execution failed in this environment due to npm registry access being blocked (403 Forbidden) so tests were not executed here.
Ran git diff --check and file/format checks completed without reported issues in this environment.

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