fix(service-rate): resolve parcel box images after production fingerprinting

[roncodes]

Problem

In the published console (fleetbase/fleetbase-console:v0.7.68), the parcel fee section of the service rate form and details panel shows broken images. /engines-dist/images/boxes/small.png returns the console's index.html (HTTP 200, text/html).

Cause

The asset path itself is correct. Because the engine is lazy, ember-engines moves its public tree under engines-dist/, and mergeWithPublicTree puts assets/ at the root of that tree, so the boxes really do land in engines-dist/images/boxes/.

The problem is fingerprinting. The console's production build runs broccoli-asset-rev, which fingerprints png, jpg, gif, js, css and map by default. The v0.7.68 image ships:

engines-dist/images/boxes/small-8bb1ab261f579043d455f1cb6a528edf.png
engines-dist/images/boxes/medium-5e0db208f3a521346e027eeaa1f84201.png
engines-dist/images/boxes/large-8733258016b7bf680507fc30b428353f.png
engines-dist/images/boxes/x-large-74c83d1fd2796caea1f6970a8bfec85a.png

broccoli-asset-rev rewrites asset URLs that appear as literal strings in JS, CSS and HTML. It can't rewrite /engines-dist/images/boxes/{{parcelFee.size}}.png because the file name is only built at runtime. The shipped engine.js still contains the bare /engines-dist/images/boxes/ prefix, so the request misses and nginx's SPA fallback serves index.html.

Fix

A new parcel-box-image helper maps each size to a literal URL, so the fingerprinter rewrites each one to its hashed name. Unknown sizes fall back to the medium box. Both service-rate/form.hbs and service-rate/details.hbs use it.

Other /engines-dist/images/... references

I checked these against the shipped v0.7.68 engine.js and engine.css. None needs a change:

Reference	In the published build
map-marker.png (widget/live-fleet.hbs)	Literal string, rewritten to map-marker-bfdcdde0….png
building-marker.png (several)	Literal string, rewritten to building-marker-aa16d468….png
drawing-controls-spritesheet-inverted.png (fleetops-engine.css)	Literal url(), rewritten to its hashed name
drawing-controls-spritesheet.svg (fleetops-engine.css)	svg isn't fingerprinted, served as is
telematics/providers/default.webp (resource-descriptors/connectivity.js)	webp isn't fingerprinted, served as is

Unrelated, but found during the audit: map/google-live-map.js falls back to /engines-dist/images/driver-marker.png and /engines-dist/images/vehicle-marker.png. Neither file exists in this package or in the published image, so those fallbacks are broken in every build. This PR leaves them alone.

Testing

I didn't run a local build. CI covers the new integration test (tests/integration/helpers/parcel-box-image-test.js). The fingerprint rewrite only happens in a production console build, so the end-to-end check is a showcase capture without the capture/fixtures/boxes override.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9ba5d0d) to head (c255ee6).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##                main      #370   +/-   ##
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  Coverage     100.00%   100.00%           
  Complexity     12379     12379           
===========================================
  Files            600       600           
  Lines          46496     46496           
===========================================
  Hits           46496     46496           

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