fix(search): match combined "Title: Subtitle" author+title queries; page author lookups at max size

[rknall]

Summary

Two related improvements to the author+title search path.

1. Correctness — combined Title: Subtitle queries (the form Library Import emits) returned zero results. Audible splits a book name across Title + Subtitle; the filter required the query to be a substring of one field individually, so the combined string matched neither and every result was dropped.
2. Performance — the author-catalogue pagination derived its page size from the result cap, so a small cap shrank pages to 10 items and prolific authors took many sequential Audible calls.

Changes

Changed

• Author and author+title lookups now page at 50 (Audible's maximum page size) instead of min(50, max(10, candidateLimit)). The aggregation loop already fetches every page until the catalogue ends, so page size never affected which results are considered — only the number of round-trips. Result: ~4× fewer Audible requests (Elfie Donnelly author+title: 13 → 3), identical result set.

Fixed

• Author+title search now matches combined Title: Subtitle queries. Matching normalizes punctuation/whitespace and also tests the combined Title Subtitle form, so a query like A Dance with Dragons: A Song of Ice and Fire, Book 5 (author George R.R. Martin) returns the book (0 → 2 in the de region) instead of nothing.

Testing

• Manual verification against a live instance with real data:
  • The combined-title query returns the book (previously 0 results).
  • The Elfie Donnelly author+title search drops from 13 → 3 Audible requests with an unchanged result set.

Notes

• Why the page size is hardcoded to 50 rather than derived from the cap: candidateLimit is a result-set bound (how many results we keep), while page size is a transport concern (items per HTTP round-trip). The loop deliberately aggregates all pages regardless of the cap, so page size has no effect on the result set — only on latency. The old formula's only effect was to make pages smaller when a caller passed a small cap (the Advanced search sends cap=5 → pageSize 10). 50 is the API maximum, any smaller value only adds round-trips, and no larger value is possible — so there is nothing worth making configurable.
• Out of scope: region-specific result differences (the same query returning the book under de but not us) are a separate regional-search concern, not addressed here.