docs: add pagination reference — offset vs cursor, nested relations

[pyramation]

Summary

Adds a dedicated pagination.md reference to the constructive-graphql skill. Previously, pagination knowledge was scattered across 5+ files with no single source of truth. This consolidates everything into one reference covering:

• The Connection model — PostGraphile's Relay-based connection type (nodes, pageInfo, totalCount)
• Offset vs cursor pagination — when to use each, with examples across all three query surfaces (ORM, React Query hooks, runtime query builder)
• Forward and backward paging — first/after and last/before
• Nested relation pagination — independent pagination on hasMany/manyToMany connections
• TypeScript types — ConnectionResult<T>, PageInfo, FindManyArgs
• Decision matrix — offset vs cursor
• Codebase reference table — maps pagination behavior to source files

Also updates SKILL.md:

• Quick Start pagination section now links to pagination.md instead of codegen-orm-patterns.md
• Reference table splits pagination into its own row

Updates since last revision

• Removed all edges content — Constructive uses nodes exclusively, so the edges discussion and decision guide were removed to avoid confusion
• Rewrote the infinite scroll React Query example to use the ORM (db.user.findMany().execute().unwrap()) instead of raw GraphQL strings
• Simplified the Connection model GraphQL example to only show nodes-based types
• Cleaned up codebase reference table to remove edge-related entries

Review & Testing Checklist for Human

• Verify the ORM code examples match actual API signatures — especially findMany args (first, last, after, before, offset), ConnectionResult shape, and .execute().unwrap() chain
• Check the infinite scroll example — confirm that db.user.findMany().execute().unwrap() returns a shape where lastPage.pageInfo.hasNextPage and lastPage.pageInfo.endCursor are directly accessible (used by getNextPageParam)
• Skim the codebase reference table at the bottom — line numbers will drift but verify the file paths and behavioral descriptions are currently accurate

Notes

• Documentation-only change, no runtime risk
• All examples use the ORM exclusively — no raw GraphQL strings

Link to Devin session: https://app.devin.ai/sessions/745d2d10b699452091e24131ba5edef2
Requested by: @pyramation

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