feat(sub12b): plant overview Racks pane (Task 16)

Controller: extend /fp/shopfloor/plant_overview return payload to
include 'racks' array (filtered to loaded/in_use/awaiting_unrack
states). Each entry has tag chips, part count, current node
breadcrumb, current step + tank code, and a precomputed
next_step_id (next sequence in the job's recipe — operator
overrides at runtime in the Move Rack dialog).

JS: state.racks populated from payload. New openMoveRackDialog()
method spawns FpMoveRackDialog. Notification when rack has no
successor (last step of job).

XML: top section above the existing work-centre columns. Renders
rack rows with tags, part count, breadcrumb, and primary MOVE RACK
button per row. Visible only when state.racks.length > 0.

SCSS: minimal styling for the racks pane (extends move_dialogs.scss
to keep all Sub 12b styles in one file).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fusion_plating/fusion_plating_shopfloor/controllers/shopfloor_controller.py

@@ -1274,11 +1274,56 @@ class FpShopfloorController(http.Controller):
                 'cards': cards_by_wc[0],
             })
 
+        # Sub 12b — Racks pane payload alongside the existing parts cards.
+        # Filters to racks currently in active racking-state. Each entry
+        # has the data the OWL plant overview's Racks pane renders:
+        # tag chips, current node breadcrumb, part count, and the
+        # rack-level MOVE RACK button target.
+        rack_domain = [
+            ('racking_state', 'in', ('loaded', 'in_use', 'awaiting_unrack')),
+            ('active', '=', True),
+        ]
+        if facility_id:
+            rack_domain.append(('facility_id', '=', int(facility_id)))
+        racks_payload = []
+        for r in env['fusion.plating.rack'].search(rack_domain):
+            cur_step = r.current_job_step_id
+            racks_payload.append({
+                'id': r.id,
+                'name': r.name,
+                'racking_state': r.racking_state,
+                'tag_ids': [
+                    {'id': t.id, 'name': t.name, 'color': t.color}
+                    for t in r.tag_ids
+                ],
+                'current_part_count': r.current_part_count,
+                'current_node_name': cur_step.name if cur_step else '',
+                'current_tank_code': (
+                    r.current_tank_id.code if r.current_tank_id else ''
+                ),
+                'current_step_id': cur_step.id if cur_step else False,
+                # Default destination: next sibling step in the recipe
+                # sequence. Falls back to current_step_id if no successor
+                # (operator can pick a different one in the dialog).
+                'next_step_id': self._fp_next_step_id(cur_step) if cur_step else False,
+            })
+
         return {
             'facility_name': facility_name,
             'columns': columns,
+            'racks': racks_payload,
         }
 
+    def _fp_next_step_id(self, step):
+        """Return the id of the next step in this job's recipe sequence,
+        or False if `step` is the last."""
+        if not step or not step.job_id:
+            return False
+        successors = step.job_id.step_ids.filtered(
+            lambda s: s.sequence > step.sequence
+        ).sorted('sequence')
+        return successors[0].id if successors else False
+
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