revert: undo chained/seed-grown track 5 frames, back to b71f1d4

Reverts 1530bbc and 9c95a4a. Track 5 Frames sends the drawn box unchanged to
all five frames - no chaining, no growth. Both were rejected: chaining let a
wrong read on one frame poison the next, and growth was an attempt to follow a
moving object that the user did not want.

REQ-189, ui-spec and tasks.md return to the b71f1d4 wording.

frontend/src/pages/ReviewPage.jsx

@@ -9,38 +9,6 @@ import ReviewSidebar from '../components/ReviewSidebar'
 import ExemplarFilterPanel from '../components/ExemplarFilterPanel'
 import useExemplarPool from '../hooks/useExemplarPool'
 
-// How much bigger the seed box gets for each frame after the first, so the
-// object has room to have moved. Hand-tuned, not learned (REQ-189). The box
-// always derives from the drawn shape — never from a previous run's result.
-const SEED_GROWTH = 1.5
-
-// SAM3 assist wants one normalized [x0, y0, x1, y1] box (REQ-043). A bbox
-// shape already is that; a polygon is reduced to its bounding box.
-function shapeBox(geometry) {
-  const pts = geometry?.points
-  if (geometry?.type === 'bbox' && pts?.length === 4) return pts
-  if (geometry?.type === 'polygon' && pts?.length) {
-    let minX = 1, minY = 1, maxX = 0, maxY = 0
-    for (const [x, y] of pts) {
-      if (x < minX) minX = x
-      if (x > maxX) maxX = x
-      if (y < minY) minY = y
-      if (y > maxY) maxY = y
-    }
-    return [minX, minY, maxX, maxY]
-  }
-  return null
-}
-
-function growBox([x0, y0, x1, y1], k) {
-  const cx = (x0 + x1) / 2
-  const cy = (y0 + y1) / 2
-  const hw = ((x1 - x0) * k) / 2
-  const hh = ((y1 - y0) * k) / 2
-  const clamp = (v) => Math.min(1, Math.max(0, v))
-  return [clamp(cx - hw), clamp(cy - hh), clamp(cx + hw), clamp(cy + hh)]
-}
-
 export default function ReviewPage({ batchId: rawBatchId, projectId, onProject }) {
   const [batch, setBatch] = useState(null)
   const [project, setProject] = useState(null)
@@ -399,8 +367,23 @@ export default function ReviewPage({ batchId: rawBatchId, projectId, onProject }
       return
     }
 
-    const firstBox = shapeBox(current.geometry)
-    if (!firstBox) {
+    // SAM3 assist wants one normalized [x0, y0, x1, y1] box (REQ-043). A bbox
+    // shape already is that; a polygon is reduced to its bounding box.
+    const geometry = current.geometry
+    let box = null
+    if (geometry?.type === 'bbox' && geometry.points?.length === 4) {
+      box = geometry.points
+    } else if (geometry?.type === 'polygon' && geometry.points?.length) {
+      let minX = 1, minY = 1, maxX = 0, maxY = 0
+      for (const [x, y] of geometry.points) {
+        if (x < minX) minX = x
+        if (x > maxX) maxX = x
+        if (y < minY) minY = y
+        if (y > maxY) maxY = y
+      }
+      box = [minX, minY, maxX, maxY]
+    }
+    if (!box) {
       setError('That shape has no usable box — Track 5 Frames needs one.')
       return
     }
@@ -417,15 +400,8 @@ export default function ReviewPage({ batchId: rawBatchId, projectId, onProject }
       const failures = []
       for (let i = 0; i < ahead.length; i++) {
         const targetFrame = ahead[i]
-        // Every frame is seeded from the drawn box, never from a previous
-        // result, so a bad read on one frame cannot carry into the next.
-        // Frames 2-5 get it grown about its centre — the object has had
-        // time to move by then.
-        const seedBox = i === 0 ? firstBox : growBox(firstBox, SEED_GROWTH)
         try {
-          await api.assist(targetFrame.id, {
-            box: seedBox, class_id: current.class_id,
-          })
+          await api.assist(targetFrame.id, { box, class_id: current.class_id })
           tracked++
           patchFrameLocally(targetFrame.id, { annotation_count: (targetFrame.annotation_count ?? 0) + 1 })
         } catch (exc) {