fix(gfql): apply GRAPH residual predicates as masks

[lmeyerov]

What

Fixes GRAPH { MATCH ... WHERE ... } residual predicate handling for the safe graph-mask cases instead of silently dropping the predicate or merely raising.

This PR compiles single-alias residual predicates into explicit graph residual-mask metadata, then applies those masks to the target node or edge frame before the graph-state Chain runs. That covers residual forms such as OR/NULL expressions and searchAny(...) for a single node or edge alias.

Pattern-predicate and multi-alias residuals still fail loudly because they need first-class projection semantics rather than a local entity mask. Polars also declines these GRAPH residual masks for now instead of silently bridging or mis-evaluating.

Why

Issue #1662 exposed a silent wrong-results bug: GRAPH constructors could accept row residual predicates from Cypher lowering, but Chain(lowered.query, where=lowered.where) had nowhere to apply them.

The root fix is to preserve the residual and apply it at graph state construction time when it is semantically a node or edge mask.

Handoff / backport notes

Use the net PR diff as the source of truth; the first commit (b1903892, fail-fast) was intentionally superseded by the later mask implementation. If cherry-picking into a branch that has moved ahead, prefer either cherry-picking the full stack or reapplying the net diff for these files:

• graphistry/compute/gfql/cypher/lowering.py: adds CompiledGraphResidualFilter, records it on compiled query/binding structs, and compiles only safe single-alias node/edge residuals.
• graphistry/compute/gfql_unified.py: applies residual masks before _chain_dispatch; pandas/cuDF path is implemented, Polars raises a clear validation error.
• graphistry/tests/compute/gfql/cypher/test_lowering.py: semantic contract for node residuals, alias/property-column collision regressions, cuDF smoke, Polars honest decline, searchAny, edge residuals, named GRAPH ... USE, and pattern-predicate rejection.
• docs/source/gfql/cypher.rst: user-facing supported/unsupported behavior.
• bin/ci_cypher_surface_guard_baseline.json: intentional internal compiled-struct surface growth.

Backport gotchas:

• Do not port only the fail-fast guard; that was the rejected interim state.
• Keep graph_residual_filters on both standalone CompiledCypherGraphQuery and named CompiledGraphBinding; otherwise GRAPH g = GRAPH { ... } USE g ... regresses.
• Keep endpoint reconciliation for node masks: after filtering nodes, filter edges to endpoints in the surviving node IDs before running the Chain.
• Keep the residual eval-frame alias marker unconditional; otherwise a real node/edge property column named like the alias (a, r, etc.) breaks alias-property residuals such as a.score / r.weight.
• Keep unsupported pattern/multi-alias residuals loud. They are not equivalent to a simple entity mask.
• If the target branch already has a native Polars row-expression graph-mask path, replace the honest Polars decline with parity tests; otherwise keep the decline test.

Surface change

The compiled Cypher structs gain one internal metadata field for GRAPH residual masks. The Cypher surface guard baseline was regenerated intentionally for:

• CompiledCypherQuery: 7 -> 8 fields
• CompiledGraphBinding: 6 -> 7 fields
• CompiledCypherGraphQuery: 6 -> 7 fields

User impact

• Native GRAPH predicates continue to work.
• Single node/edge residual predicates inside GRAPH { } now filter the returned subgraph on pandas/cuDF.
• searchAny(...) works in the supported single-alias GRAPH mask form.
• Unsupported pattern/multi-alias residuals still fail clearly instead of returning wrong results.
• Polars GRAPH residual masks fail clearly pending native support.

Validation

• python bin/ci_cypher_surface_guard.py -> passed
• python -m pytest -q graphistry/tests/compute/gfql/cypher/test_lowering.py -k 'graph_constructor or graph_binding_applies_residual_mask_before_use' -> 17 passed
• python -m pytest -q graphistry/tests/compute/gfql/test_engine_polars_conformance_matrix.py -k 'prune_isolated_graph_shape' -> 1 passed
• python -m pytest -q graphistry/tests/compute/gfql/test_viz_pipeline_conformance.py -k 'graph_state_prune_pipeline' -> 1 passed
• python -m ruff check graphistry/compute/gfql/cypher/lowering.py graphistry/compute/gfql_unified.py graphistry/tests/compute/gfql/cypher/test_lowering.py -> passed

Refs #1662