ADR-013 Phase 3: generic asset-panels renderer (Path A)

Wires the ADR-010 get_asset_panels hook to a generic frontend renderer so a
plugin adds detail-page UI as JSON, no Vue. This is the Path A foundation that
lets simple plugins ship UI without a frontend build.

- components/PluginAssetPanels.vue + pluginAssetPanels.js: fetches
  /api/pluginui/asset-panels for an asset, then each panel's data endpoint, and
  renders by mode: list (title + status badge + meta lines via a field map),
  keyvalue, table (declared or inferred columns), badge. Pure mapping logic is
  in the .js module and unit tested (9 specs), same pattern as entryForm.js.
- New 'list' render mode with a declarative field map (title/badge/meta),
  documented on the hook in base.py.
- Warranty migrated to it: get_asset_panels now declares a 'list' panel + map
  that reproduces WarrantyPanel's output (vendor title, status badge with color
  + label map, servicelevel/ends/tag meta, manage link) with zero
  warranty-specific frontend code.
- MachineDetail swapped from <WarrantyPanel> to <PluginAssetPanels> (pilot); the
  hero warranty badge is unchanged. Verified end to end: the API serves the list
  panel + map and the warranty rows; the page renders without error.

Rollout of the other 4 detail pages (PCDetail, PrinterDetail, NetworkDeviceDetail,
MeasuringToolDetail) and the map-overlays / asset-presentation renderers are
follow-up Phase 3 commits. 58 vitest, build clean, 1067 backend pass, naming green.

shopdb/plugins/base.py

@@ -297,7 +297,9 @@ class BasePlugin(ABC):
             'title':      str,        # panel heading
             'assettypes': List[str],  # AssetType keys it appears on; ['*'] = all
             'endpoint':   str,        # data endpoint (may contain {assetid})
-            'render':     str,        # 'keyvalue' | 'table' | 'badge'
+            'render':     str,        # 'keyvalue' | 'table' | 'badge' | 'list'
+                                      # ('list' takes a 'map' of title/badge/meta
+                                      # keys, rendered generically - see warranty)
             'position':   int,        # order among panels
         }