Add Hot kernel catalogue and spatial baseline fallback

[Valessc2]

S09-S14

Builds the first real Hot catalogue while preserving baseline/OFF authority.

• moves the neutral UnitView/WorldView contract into sc2opt::model so Kernel never depends on Adapters
• adds explicit strict/inclusive boundary semantics for geometry/range/facing
• adds caller-owned unit filtering
• adds exact brute-force radius-query baseline
• adds reusable SpatialGrid2D candidate inspired by MMEvo Z2, with retained bucket storage and exact filtering
• supports stable source-order or explicitly unordered spatial results
• adds SpatialCrossoverProfile whose default thresholds keep the grid OFF until certified
• adds deterministic equivalence/regression tests including exact-boundary cases
• adds a synthetic spatial calibration executable that includes rebuild cost and is compiled, but not timing-gated, in CI

Safety / cheapness

No crossover threshold is guessed. size_t::max() means not certified, so brute force remains champion. CI timing is never used to promote a runtime strategy. Stable-order mode exists specifically to avoid the ordering/boundary regressions found during the MMEvo Z audit.

Validation

Draft until Linux/Windows C++ and Python CI prove the published tree; benchmark code is compiled but deliberately not used as a performance gate.