docs(gfql): Rename chain() to gfql() throughout documentation

[lmeyerov]

Summary

This PR renames all chain() and chain_remote() method calls to gfql() and gfql_remote() throughout the documentation, implementing the deprecation announced in the CHANGELOG.

Changes

Method Renames

• ✅ Renamed all g.chain() references to g.gfql()
• ✅ Renamed all g.chain_remote() references to g.gfql_remote()
• ✅ Updated method references in spec documentation
• ✅ Preserved Chain class references (not method calls)

Documentation Updates

• ✅ Added migration notes to CHANGELOG.md with clear before/after examples
• ✅ Updated 15 documentation files across:
  • User guides (cheatsheet, 10min, overview, etc.)
  • GFQL documentation (about, combo, quick, remote, etc.)
  • Specification files (language, python_embedding, wire_protocol, cypher_mapping)
  • Example files (datetime_filtering, wire_protocol_examples)

Migration Guide

Added to CHANGELOG.md:

### Breaking 🔥
* GFQL: Renamed `chain()` methods to `gfql()` for clarity
  * **Migration required**: Update your code as follows:
    * `g.chain([...])` → `g.gfql([...])`
    * `g.chain_remote([...])` → `g.gfql_remote([...])`
  * The Chain class itself remains unchanged
  * This change makes the API more intuitive as 'gfql' directly indicates Graph Frame Query Language operations

Process

• Each change was manually inspected for semantic correctness
• No automated find/replace was used to ensure quality
• Chain class references were preserved (only method calls were renamed)

Related PRs

• Based on PRs feat(gfql): Add comprehensive GFQL implementation with let/ref/call/remote #744 and docs: Add auto-generated API documentation for GFQL classes (rebased from #742) #745 (already merged)
• Incorporates improvements from PR docs(gfql): Consolidated GFQL documentation improvements #719

Testing

• Documentation builds successfully
• All examples use correct new syntax
• Migration guide is clear

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com