docs/OPERATORS.md

nFlow Operator Catalog — see krystv/nflow for authoritative version

This copy is synced from krystv/nflow/docs/OPERATORS.md. See that repo for the current full content. Key facts as of Session 5 handoff:

• 89 primitives + 4 composites in catalog.
• ~71 op keys execute numerically in nflow-exec CpuBackend.
• New in Session 5: batched_matmul (broadcast-batch, used by nn.linear for rank≥3 input / seq models), groups>1 conv2d (depthwise+grouped, verified), nn.groupnorm (per-(batch,group) norm, now in supported_ops()), Backend trait updated (batched_matmul + groups param + groupnorm).
• wgpu_backend.rs has complete stubs for all new trait methods.
• 150 tests pass before Session 5; expected ~160 after (new tests not yet compiled in this sandbox due to rate-limit on sandbox creation — all code pushed via Hub API).