Fix: path parameters must always be required per OpenAPI spec

[renardeinside]

Summary

• Enforce required: true for path parameters in normalize_param(), per the OpenAPI 3.0 spec which mandates path params are always required
• Fixes issue where FastAPI-generated specs omit required for path params (since it's implied), causing generated TypeScript hooks to treat params as optional and producing tsc errors under strict: true
• Add test verifying path params without explicit required field generate non-optional TypeScript params

Closes #79

Test plan

• cargo test -p apx-core openapi — all 103 tests pass
• just fmt — clean
• just check — all checks pass
• New test test_path_params_required_even_when_omitted validates fetch function and hook signatures

🤖 Generated with Claude Code