Reject source grids that don't share a horizontal lattice (#547)

[amarcozzi]

Summary

Closes #547. irradiance.surface.relative (LeafLux) and fuel_moisture.dead.1hr (Fosberg) each derive an output by combining two source grids cell-for-cell inside a processing service (treevox, griddle). Both endpoints assumed the two grids already shared a horizontal lattice and passed the raw arrays straight through — so a mismatch (the common case: a fine 2 m LAD grid paired with a coarse 30 m terrain grid) surfaced only as an async worker crash:

ValueError: Terrain dimensions must match leaf area grid dimensions.
Leaf area is (715, 703) and terrain is (173, 141)

The job failed with UNEXPECTED_FAILURE and no actionable message. Confirmed against treevox-v2-prod logs (multiple occurrences). This was blocking end-to-end validation of the Fosberg 1-hr dead fuel moisture grid (#540).

Approach

Catch the mismatch synchronously at the API boundary with a clear 422, and keep the processing services' existing pre-aligned-input contract intact (no resampling pushed into treevox/griddle).

• New shared validator validate_grids_share_horizontal_lattice in grids/utils.py: compares two grids' CRS (via lib.crs.crs_equal), trailing (y, x) shape, and the six affine-transform coefficients (abs tol 1e-9). A 3D grid may pair with a 2D grid — only the horizontal lattice must match. Returns 422 with resample remediation guidance.
• LeafLux router — validates the terrain grid against the LAD grid; also scopes both source lookups to the domain (a cross-domain source grid now 404s, where the LAD lookup previously wasn't domain-scoped).
• Fosberg router — validates the irradiance grid against the topography grid (whose georeference the output inherits).
• Compose router — already enforced this inline; now delegates to the shared validator. Behavior-preserving: compose grids are always 2D (_shape_rank), so shape[-2:] equals the full shape.
• OpenAPI field descriptions for both endpoints now state the same-lattice requirement and how to resample.

Validation runs before the output document is written or a task dispatched, so a rejected request creates no grid and dispatches no worker.

Tests

• New validate_grids_share_horizontal_lattice unit tests (matching 3D/2D, equivalent CRS spellings, and CRS / shape / transform mismatches).
• LeafLux + Fosberg router regression tests: aligned success, 3D-irradiance-with-matching-y/x success, cross-domain 404, and shape/transform/CRS mismatch → 422.
• Compose validate-alignment tests extended for shape and transform.

Verified locally against a live API server: unit tests 28 passed; router tests (LeafLux + Fosberg + Compose) 86 passed; ruff check / ruff format --check clean.

Contract / downstream notes (Beta)

1. API contract — two new synchronous rejections: mismatched-lattice terrain/irradiance now 422s (instead of a downstream async failure), and a cross-domain LeafLux source grid now 404s. Correct hardening; flagging as a conscious Beta break.
2. SDK — silvxlabs/fastfuels-sdk-python#197 is held pending this fix; the SDK/docs should note that terrain/irradiance must share the consumer grid's lattice (422 otherwise). OpenAPI descriptions updated here.