fix(assets): serve leaflet marker icons from the leaflet package

[janni1288]

What

Several components (leaflet-map-manager.js, map-adapter/leaflet.js, map-adapter/google.js, order-tracking-lookup.js, customer/create-order-form.js, customer/orders.js) reference assets/images/marker-icon.png, marker-icon-2x.png and marker-shadow.png for Leaflet's default markers. These files were never added to the addon's public assets, so the browser gets 404s and shows broken image icons on the map.

Why this approach

Rather than committing copies of these images into the repo (which would drift out of sync with the installed Leaflet version over time), this serves them directly from the already-installed leaflet package via a broccoli-funnel tree - the same pattern already used in index.js for leaflet-draw and leaflet-contextmenu's dist assets.

Changes

• index.js: new treeForLeafletImages() funnels marker-icon.png, marker-icon-2x.png, and marker-shadow.png from leaflet/dist/images into assets/images, wired into mergeWithPublicTree
• package.json: added leaflet as a direct dependency - it was previously only resolved transitively via leaflet-draw/leaflet-contextmenu, which caused resolve.sync to fail when referenced directly

Testing

• Verified locally that all three URLs now serve the correct images instead of 404ing:
  • /assets/images/marker-icon.png
  • /assets/images/marker-icon-2x.png
  • /assets/images/marker-shadow.png

Verification of scope

Searched the addon for all /assets/images/* references to check whether
other assets were missing besides the three named in the issue — these
three were the only ones referenced in code but missing from the assets
folder, so this should be the complete fix.

Closes #211

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (41bd574) to head (8acbf62).
⚠️ Report is 297 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff               @@
##               main      #289       +/-   ##
==============================================
+ Coverage     85.97%   100.00%   +14.02%     
  Complexity     9766      9766               
==============================================
  Files           521       521               
  Lines         37782     37762       -20     
==============================================
+ Hits          32483     37762     +5279     
+ Misses         5299         0     -5299     

Flag	Coverage Δ
backend	100.00% <ø> (+14.02%)	⬆️

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