test: push Cli line coverage from 90% to 94%

[Theauxm]

Summary

Adds coverage for OpenAPI edge cases and a GraphQL fallback that were sitting uncovered:

• OpenAPI: allOf with $ref, allOf without $ref (object fallback), oneOf/anyOf with $ref, oneOf/anyOf with primitives (object fallback), additionalProperties (Dictionary mapping), all scalar formats (uuid, uri, binary, date, date-time, float), untyped fallback, allOf field merging across schemas, operationId collisions disambiguated by path parameters.
• GraphQL: operations whose return type isn't defined fall back to `object` with a TODO description.

Two compact fixtures (`openapi-edge-cases.json`, `graphql-unknown-type.graphql`) drive six tests. Local line coverage moves from 90.4% to 94.2%; the remaining gaps are mostly defensive throws in `TraxProjectGenerator.RunDotnetNew` and `IsDotnetAvailable` (env-dependent), unreachable switch-default arms, and the top-level `Program.cs` entry point.

Test plan

• `dotnet test tests/Trax.Cli.Tests` — all passing (6 new)
• `dotnet csharpier check .` — clean

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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