fix(qwen36): advertise existing gateway tool support

[Altroo]

Summary

Qwen tool rendering and parsing landed in #1794, but the qwen36 family still publishes capabilities.tools=false. Clients using the public metadata can therefore disable tools even though the gateway supports them.

Set only that capability flag and add a regression test against public_metadata. No engine, parser, template, or other capability changes.

Validation

• env -u OMP_NUM_THREADS make -C c -j4 check: clean portable CPU build and C tests passed; 2,402 Python tests ran, 305 skipped, no failures.
• git diff --check passed.
• Validated on Apple Silicon/macOS against upstream dev 88f25a60.
• No CUDA changes or performance claims.

Compatibility

• Default CPU build remains dependency-free.
• No model files, generated binaries, or benchmark artifacts included.

Related: #1794 (implemented tool calling); this corrects its remaining registry metadata mismatch.