Add backend pagination and filtering for all hosted and remote instance list endpoints

Some of our instance listing endpoints load everything in one go and leave pagination/filtering to the frontend. This doesn't scale and we should move to proper backend pagination and filtering across the board.

## Current state

* `GET /api/v1/teams/:teamId/projects` already supports `page`, `limit`, `query`, `sort`, `dir`, and `state` filtering. The team hosted instances page (`pages/team/Instances.vue`) uses these.
* `GET /api/v1/applications/:applicationId/instances` has **no pagination support at all**. It loads every instance via `Project.byApplication()` and returns a flat `{ count, instances }` response with no pagination metadata.
* `GET /api/v1/teams/:teamId/devices` and `GET /api/v1/projects/:instanceId/devices` already support full pagination, search, sort, and filter parameters. These are in good shape.
* Application-level device listing goes through the team endpoint with context filtering, which also works.

## What needs to happen

* Add pagination, search, sorting, and status filtering to `GET /api/v1/applications/:applicationId/instances` to match what the team-level endpoint already supports
* Audit the team-level instances endpoint to make sure its filtering capabilities are complete (it supports `state` filtering but might be missing other useful filters)
* Update the frontend pages to use server-side pagination instead of loading all instances
* Make sure both hosted and remote instance lists across all contexts (team level, application level) consistently use backend pagination

**Note:** Application-level pagination is out of scope for now. This is focused on the instance/device list endpoints within those contexts.

This is a prerequisite for the other hosted/remote instance unification efforts since proper filtering and pagination on the backend is needed before the UI work can land cleanly.