fix(models): declare relation return types the console requests

[roncodes]

Companion to fleetbase/core-api#303, which only lets a client's with / expand / with_count name a method that declares an Eloquent Relation return type, or one listed in $withable. Before #303, any public method with no required arguments could be called through with, for example with[]=saveInstance inserted a blank row.

Under #303, these relations would stop loading because the console requests them and they have no return type. This PR adds the return types:

Model	Method	Type	Console request
Store	networks	BelongsToMany	store switcher (routes/application.js)
Product	addonCategories, variants, files, hours	HasMany	product edit
ProductAddonCategory	category	BelongsTo	product model
ProductVariant	options	HasMany	product model
StoreLocation	hours	HasMany (its docblock wrongly said BelongsTo)	home, settings

Merge order: merge this with #303 or before it. On today's core it changes nothing at runtime.

Fatal-error check: adding a return type is fatal for any subclass that overrides the method without one. I scanned every package for subclasses of these five models, following extends chains transitively and matching names case-insensitively, plus anonymous test subclasses. None override a typed method. No core parent or trait defines these names.

API / docs: no change in behaviour, so no fleetbase/postman or fleetbase.io update.

Other storefront with requests:

• orders/index/view.js sends a with list that OrderController::findRecord ignores.
• alertIncomingOrder requests fleetops Order relations (customer, payload, trackingNumber), which are already typed.
• storefront-app's with: ['locations'] reaches NetworkController@stores, which uses fixed relations.

Validation

• php -l on the 5 files: clean.
• php-cs-fixer dry-run on the 5 files: clean.
• php scripts/pest-runner.php server/tests: 689 tests, 0 failures, 23 errors. The base commit gives the same 23 errors in the same worktree. The local vendor copy lacks Fleetbase\Support\SocketCluster\* and Illuminate\Validation\Factory, so these errors are not from this change.
• Each class loads through the autoloader, and reflection reports the declared types.

Tests: I added no new tests. The relation filtering is tested in core-api #303, and this PR only adds declarations.