Add first-class Trailer operations

[roncodes]

Summary

• introduce Trailer as a first-class Fleet-Ops resource backed by the Asset base with a Trailer discriminator and public ID namespace
• add full Fleet-Ops navigation, list/grid/detail/create/edit flows directly below Vehicles
• add effective-dated towing connections with conflict-safe attach/detach behavior and Vehicle views
• generalize Device and Equipment attachment to support Trailer polymorphism and installation history
• add Trailer telematics ingestion, stale-event protection, positions, connectivity state, and tenant-safe broadcasts
• integrate Trailer maintenance, work orders, custom fields, import/export, search, reporting, AI query resources, permissions, and translations
• add public and internal Trailer routes, filtering, resources, validation, and focused contract tests

Validation

• pnpm lint:hbs
• pnpm lint:js
• pnpm lint:intl
• focused PHP tests pass for Trailer model/broadcast behavior, Equipment polymorphism, telematics, Device API contracts, and public Trailer endpoint contracts
• PHP formatting check passes for the changed PHP files
• production Ember build passed during implementation; a final local rerun was affected by the sandbox process-uptime restriction after compilation

Baseline limitations

• the full PHP unit suite reaches an existing unrelated Service Quote controller test failure
• repository-wide PHPStan reports the existing package baseline
• bulk delete is intentionally not included; deleting one attached Trailer returns a conflict until it is detached
• the Asset public ID migration is nullable and does not rewrite historical Asset rows

Related PRs

• fleetops-data: Add first-class Trailer data models fleetops-data#75
• Postman: Add Trailer API lifecycle collection postman#58
• fleetbase.io: Document first-class Trailer operations fleetbase.io#96

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a9131da) to head (c5a6211).

Additional details and impacted files

@@             Coverage Diff              @@
##                main      #309    +/-   ##
============================================
  Coverage     100.00%   100.00%            
- Complexity      9899     10083   +184     
============================================
  Files            526       538    +12     
  Lines          38163     38802   +639     
============================================
+ Hits           38163     38802   +639     

Flag	Coverage Δ
backend	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.