feat(graphql-codegen): make React Query optional with config flag

[pyramation]

Summary

Adds a reactQuery.enabled configuration option to control whether React Query hooks are generated. When disabled (the default), only standalone fetch functions are generated, removing the React/React Query dependency from generated code.

Key changes:

• New reactQuery.enabled config option (defaults to false)
• Query generators conditionally skip useQuery hooks and React Query imports when disabled
• Mutation generators return null when disabled (mutations require React Query)
• Standalone fetchXxxQuery functions are always generated regardless of setting
• README updated to fix incorrect package name (@constructive-io/graphql-sdk → @constructive-io/graphql-codegen) and added header/badges to match other packages

Review & Testing Checklist for Human

• BREAKING CHANGE: Verify that reactQuery.enabled: false as the default is intentional. Existing users upgrading will no longer get React Query hooks unless they explicitly set reactQuery: { enabled: true } in their config.
• Verify mutation behavior is acceptable: when React Query is disabled, NO mutation files are generated at all (not just hooks removed)
• Test full codegen pipeline end-to-end with both reactQuery.enabled: true and reactQuery.enabled: false to ensure generated code compiles and works correctly
• Confirm the README package name fix from @constructive-io/graphql-sdk to @constructive-io/graphql-codegen is correct

Recommended test plan:

1. Run codegen against a real PostGraphile endpoint with reactQuery: { enabled: false }
2. Verify generated query files have fetchXxxQuery but no useXxxQuery or React Query imports
3. Verify no mutation files are generated
4. Run codegen with reactQuery: { enabled: true } and verify hooks are generated
5. Ensure generated TypeScript compiles without errors in both cases

Notes

Link to Devin run: https://app.devin.ai/sessions/87a0177b0e6a4c6cbd85f27e62e732df
Requested by: Dan Lynch (@pyramation)

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