docs(gfql): cheatsheet recommends callable predicates that validation rejects #2169

At master 599c405a234bff2402e4f76041cac6e169f6f7c8, the GFQL cheatsheet documents callable values in filter_dict and recommends n({"age": lambda x: x > 30}). That example fails on both pandas and native Polars with GFQLTypeError (type-mismatch), which correctly recommends gt(5) or simple values.

Reproduce with a graph bound to a nodes dataframe containing id and age, then run g.gfql([n({"age": lambda x: x > 30})], engine="pandas") or the equivalent native Polars graph. Source: docs/source/gfql/quick.rst, Node Matchers/Edge Matchers; the documented condition_function shapes also need correction.

This docs correction is independent of #967, which requests restoring local lambda support. Keep that feature request open.

Acceptance:

• Replace unsupported callable examples/prose with supported declarative predicates such as gt(30).
• Run the corrected node/edge examples against pandas and eager Polars with expected rows; preserve structured rejection of unsupported callables.
• Keep local query examples independent of visualization-server credentials; no runtime or remote serialization changes.