feat: add native forward cursor pagination

[hadrien]

Problem

• Offset pagination provides no cursor-based continuation.

Solution

• Add CursorPage, CursorPaginate, and a configurable native SQLAlchemy paginator.
• Use next_cursor as the only continuation metadata.
• Support composite ordering, mixed directions, ORM entities, and column projections.
• Validate typed cursor values before querying.
• Preserve offset pagination without adding dependencies.
• Document validated POST searches with pagination, filters, and ordering in JSON.

Next

• N/A

Bead: fs-i5c

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.77%. Comparing base (b746622) to head (5d0262e).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #164      +/-   ##
==========================================
+ Coverage   97.74%   98.77%   +1.03%     
==========================================
  Files           1        1              
  Lines         133      245     +112     
  Branches        7       29      +22     
==========================================
+ Hits          130      242     +112     
  Misses          3        3              

Flag	Coverage Δ
fastapi-post121	98.77% <100.00%> (+1.03%)	⬆️
fastapi-pre121	98.77% <100.00%> (+1.03%)	⬆️
sqlmodel	98.77% <100.00%> (+1.03%)	⬆️

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