Paginate Fleet-maintained apps and filters (#47615)

Fix the Fleet-maintained apps list being cut off by adding server-side
pagination and applying platform / "hide added apps" filters across the
full library. Introduces MaintainedAppListOptions (with Platform and
AvailableOnly) and changes the ListAvailableFleetMaintainedApps /
ListFleetMaintainedApps signatures. Datastore now paginates and counts
by distinct app name, fetches all platform rows for apps on a page, and
returns a count and pagination metadata; default client page size set to
500. Frontend no longer performs client-side filtering or local
status/platform state; it relies on the API and uses data.count for
totals. Docs, tests, mocks, and various call sites updated (including a
new test that verifies pagination, platform and availability filters).

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

- [ ] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements), JS
inline code is prevented especially for url redirects, and untrusted
data interpolated into shell scripts/commands is validated against shell
metacharacters.
- [ ] Timeouts are implemented and retries are limited to avoid infinite
loops
- [ ] If paths of existing endpoints are modified without backwards
compatibility, checked the frontend/CLI for any necessary changes

## Testing

- [x] Added/updated automated tests
- [ ] Where appropriate, [automated tests simulate multiple hosts and
test for host
isolation](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/reference/patterns-backend.md#unit-testing)
(updates to one hosts's records do not affect another)

- [x] QA'd all new/changed functionality manually

For unreleased bug fixes in a release candidate, one of:

- [ ] Confirmed that the fix is not expected to adversely impact load
test results
- [ ] Alerted the release DRI if additional load testing is needed

## Database migrations

- [ ] Checked schema for all modified table for columns that will
auto-update timestamps during migration.
- [ ] Confirmed that updating the timestamps is acceptable, and will not
cause unwanted side effects.
- [ ] Ensured the correct collation is explicitly set for character
columns (`COLLATE utf8mb4_unicode_ci`).

## New Fleet configuration settings

- [ ] Setting(s) is/are explicitly excluded from GitOps

If you didn't check the box above, follow this checklist for
GitOps-enabled settings:

- [ ] Verified that the setting is exported via `fleetctl
generate-gitops`
- [ ] Verified the setting is documented in a separate PR to [the GitOps
documentation](https://github.com/fleetdm/fleet/blob/main/docs/Configuration/yaml-files.md#L485)
- [ ] Verified that the setting is cleared on the server if it is not
supplied in a YAML file (or that it is documented as being optional)
- [ ] Verified that any relevant UI is disabled when GitOps mode is
enabled

## fleetd/orbit/Fleet Desktop

- [ ] Verified compatibility with the latest released version of Fleet
(see [Must
rule](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/workflows/fleetd-development-and-release-strategy.md))
- [ ] If the change applies to only one platform, confirmed that
`runtime.GOOS` is used as needed to isolate changes
- [ ] Verified that fleetd runs on macOS, Linux and Windows
- [ ] Verified auto-update works from the released version of component
to the new version (see [tools/tuf/test](../tools/tuf/test/README.md))


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Fleet-maintained apps listing now paginates server-side (100 per page)
so entries near the end of the alphabet are reachable.
* Platform and “Hide added apps” filters are applied across the entire
library, not just the currently loaded subset.
* The displayed count now matches results by counting macOS and Windows
versions separately.

* **New Features**
* Listing now supports URL-driven platform and “available” filtering,
and the UI consistently reflects the active filter state.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

docs/REST API/rest-api.md

@@ -11764,8 +11764,13 @@ List available Fleet-maintained apps.
 | Name | Type | In | Description |
 | ---- | ---- | -- | ----------- |
 | fleet_id  | integer | query | If specified, each app includes the `software_title_id` if the software has already been added to that fleet.  |
-| page     | integer | query | Page number of the results to fetch.  |
-| per_page | integer | query | Results per page.  |
+| query | string | query | Search query keywords. Searches app name. |
+| order_key | string | query | What to order results by. Currently only `name` is supported. |
+| order_direction | string | query | **Requires `order_key`**. The direction of the order. Options are `"asc"` and `"desc"`. Default is `"asc"`. |
+| page     | integer | query | Page number of the results to fetch. Pagination is by app: an app's macOS and Windows entries are counted as one result and always returned on the same page.  |
+| per_page | integer | query | Results (apps) per page.  |
+| platform | string | query | Filter to apps available on a platform. Options are `"darwin"` (macOS) and `"windows"`. |
+| available | boolean | query | If `true`, only return apps that have not yet been added to the fleet. Requires `fleet_id`. |
 
 #### Example
 
@@ -11804,6 +11809,7 @@ List available Fleet-maintained apps.
     },
     ...
   ],
+  "count": 250,
   "meta": {
     "has_next_results": false,
     "has_previous_results": false
@@ -11811,6 +11817,8 @@ List available Fleet-maintained apps.
 }
 ```
 
+> `count` is the total number of Fleet-maintained apps matching the query. An app's macOS and Windows versions are counted separately, even though the UI combines them into a single row.
+
 ### Get Fleet-maintained app
 
 Returns information about the specified Fleet-maintained app.