fix(codegen): convert string concatenation to Babel AST and template-copy patterns

[pyramation]

fix(codegen): convert string concatenation to Babel AST and template-copy patterns

Summary

This PR supersedes #689 and carries forward its ORM-as-core architecture while fixing an AST regression: 4 hook generator files (queries.ts, mutations.ts, custom-queries.ts, custom-mutations.ts) used lines.push() string concatenation instead of proper Babel AST generation. This PR converts them back.

Changes:

1. Converted 4 files from lines.push() → Babel AST (@babel/types + @babel/generator):

   • queries.ts (239 lines.push calls removed) — list + single query hooks, fetch, prefetch
   • mutations.ts (157 calls) — create, update, delete mutation hooks
   • custom-queries.ts (195 calls) — custom query hooks with variable handling
   • custom-mutations.ts (47 calls) — custom mutation hooks

2. Converted 2 files from string template literals → template-copy pattern:

   • client.ts → reads from new templates/hooks-client.ts
   • selection.ts → reads from new templates/hooks-selection.ts

3. New shared helper library (hooks-ast.ts, ~875 lines) — Reusable Babel AST node builders for imports, type references, function declarations, query/mutation patterns, etc.

4. Added AGENTS.md in graphql/codegen/ documenting three codegen rules: AST-only generation, no string concatenation, static templates as real files.

5. 22 test snapshots updated — formatting-only changes (Babel's multi-line type literals, semicolons in type properties, double quotes). No logic changes.

Review & Testing Checklist for Human

• Verify hooks-ast.ts correctness — This 875-line helper library is entirely new. Check that helper functions like buildFindManyCallExpr, returnUseQuery, buildMutationResultType produce valid AST. Note: uses @ts-ignore for Babel type parameter hacks.
• Run codegen against a real schema — Unit tests only verify snapshots. Generate hooks against an actual GraphQL endpoint/schema to confirm output compiles and works at runtime.
• Check template file resolution — findTemplateFile() traverses up directories looking for templates/. Verify this works in production builds (dist/) not just source.
• Confirm zero lines.push() remains — Search the 4 converted files to ensure no string concatenation code generation remains.
• Review snapshot diffs — The 22 updated snapshots should only show whitespace/formatting changes, not logic changes.

Recommended test plan:

1. Run pnpm build in graphql/codegen
2. Run pnpm test to verify all 204 tests pass
3. Generate hooks against a test schema: cnc codegen --react-query --endpoint <url> --output ./test-output
4. Verify generated files compile with tsc --noEmit

Notes

This PR includes all changes from the base branch feat/graphql-codegen-orm-core (the ORM-as-core refactor from PR #689), plus the AST regression fixes. The workflow file changes and test-app additions are from that base branch.

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Link to Devin run: https://app.devin.ai/sessions/a93d427c49214dce877d1fedee950c04
Requested by: @pyramation

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