feat: rename pagination default page-size option

[hadrien]

Problem

• min_page_size names a default while the accepted lower limit remains 1.
• Invalid page-size relationships fail only when FastAPI handles a request.
• Pagination examples expose the misleading name and an invalid README integration pattern.

Solution

• Add default_page_size while retaining positional behavior.
• Accept min_page_size with a caller-directed deprecation warning.
• Reject conflicting names and invalid page-size bounds during construction.
• Cover active, deprecated, positional, lower-limit, and invalid configurations.
• Update README, troubleshooting, and bundled pagination skill examples.
• Closes Rename min_page_size to default_page_size #116.

Bead: fs-i99

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.74%. Comparing base (3fef256) to head (58a7c47).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #127      +/-   ##
==========================================
+ Coverage   97.39%   97.74%   +0.35%     
==========================================
  Files           1        1              
  Lines         115      133      +18     
  Branches        2        7       +5     
==========================================
+ Hits          112      130      +18     
  Misses          3        3              

Flag	Coverage Δ
fastapi-post121	97.74% <100.00%> (+0.35%)	⬆️
fastapi-pre121	97.74% <100.00%> (+0.35%)	⬆️
sqlmodel	97.74% <100.00%> (+0.35%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.