bound change detection to the operator's selection

Change detection was the one analysis that ignored the selection entirely. It
compared two datasets in full, loaded every feature of both into Python with no
spatial predicate, and — with include_unchanged defaulting to true — returned a
FeatureCollection holding both datasets. For a regional building layer that is
the wrong answer to "what changed here" and a response no browser should be
asked to hold.

It now accepts bbox and area_id, resolved the way every other analysis resolves
them, and loads through an indexed ST_Intersects predicate.

Features are deliberately not clipped to the selection. A change class
describes a whole object: comparing a clipped earlier footprint against an
unclipped later one would report the selection edge itself as a change. Objects
the edge crosses are compared in full and counted in a warning.

The returned geometry is capped by preview_limit, spending that budget on
modified, added and removed before unchanged, while every count still describes
the whole selection.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/app/api/routes/analysis.py

@@ -36,7 +36,11 @@ def run_change_detection(
             source_dataset_id=payload.source_dataset_id,
             target_dataset_id=payload.target_dataset_id,
             iou_threshold=payload.iou_threshold,
+            modified_threshold=payload.modified_threshold,
             include_unchanged=payload.include_unchanged,
+            bbox=payload.bbox.model_dump() if payload.bbox is not None else None,
+            area_id=payload.area_id,
+            preview_limit=payload.preview_limit,
         ).model_dump(mode="json"),
     )
     return envelope(job)