fix(contributors): tolerate search results exceeding the 1,000 cap

[Eomm]

Problem

The website build fails in CI:

Error: pr search exceeds 1,000 results on 2026-09-01
    at fetchGraphqlSearchRange (scripts/contributors/collect.mjs:118:10)

When a date range returns more than 1,000 results the collector splits it in
half and retries. Once the range is a single day it cannot be split further, so
it threw and aborted the whole build.

Change

Both cap branches (REST commit search and GraphQL PR/issue search) now:

• log a warning instead of throwing when the range can't be split further;
• keep the first 1,000 results (pagination stops at the cap);
• relax the "returned N of M results" completeness assertion for that truncated
  range only — full ranges still fail loudly as before.

The build continues with slightly incomplete contributor data for the offending
day, and the CI log shows why.

[ilteoood]

The 1000 is the limit that the GitHub api can return within a single request.
The previous implementation, fixed with #499, included every update and that could easily grow. Now we check only merge and opened PR in a day.