refactor(api): implement centralized tag collection

Create a dedicated `tags` collection to centralize tag management across
the application. This replaces the previous string-based tag association
with a reference-based model using tag IDs.

The schema for a tag is as follow:
```json
{
    "_id": ObjectId,
    "tenant_id": String,
    "created_at": Time,
    "updated_at": Time,
    "name": String
}
```

Update all tag-related collections to use tag IDs instead of tag names.
A migration handles the conversion of existing tag data to the new
format.

API response format now includes tag objects:
```json
{
    ...
    "tags": [
        { "name": String },
        { "name": String },
        { "name": String }
    ]
}
```

Implement generic tag management methods in the store layer to handle
tag operations (push/pull) consistently across all taggable collections.
Add new query options to filter items by tags.

Introduce dual tag representation in taggable entities:
- TagsID: Internal array of tag IDs (not exposed via API)
- Tags: Array of models.Tag objects for API responses

api/routes/device.go

@@ -19,9 +19,6 @@ const (
 	OfflineDeviceURL            = "/devices/:uid/offline"
 	LookupDeviceURL             = "/lookup"
 	UpdateDeviceStatusURL       = "/devices/:uid/:status"
-	CreateTagURL                = "/devices/:uid/tags"      // Add a tag to a device.
-	UpdateTagURL                = "/devices/:uid/tags"      // Update device's tags with a new set.
-	RemoveTagURL                = "/devices/:uid/tags/:tag" // Delete a tag from a device.
 	UpdateDevice                = "/devices/:uid"
 )
 
@@ -243,57 +240,6 @@ func (h *Handler) UpdateDeviceStatus(c gateway.Context) error {
 	return c.NoContent(http.StatusOK)
 }
 
-func (h *Handler) CreateDeviceTag(c gateway.Context) error {
-	var req requests.DeviceCreateTag
-	if err := c.Bind(&req); err != nil {
-		return err
-	}
-
-	if err := c.Validate(&req); err != nil {
-		return err
-	}
-
-	if err := h.service.CreateDeviceTag(c.Ctx(), models.UID(req.UID), req.Tag); err != nil {
-		return err
-	}
-
-	return c.NoContent(http.StatusOK)
-}
-
-func (h *Handler) RemoveDeviceTag(c gateway.Context) error {
-	var req requests.DeviceRemoveTag
-	if err := c.Bind(&req); err != nil {
-		return err
-	}
-
-	if err := c.Validate(&req); err != nil {
-		return err
-	}
-
-	if err := h.service.RemoveDeviceTag(c.Ctx(), models.UID(req.UID), req.Tag); err != nil {
-		return err
-	}
-
-	return c.NoContent(http.StatusOK)
-}
-
-func (h *Handler) UpdateDeviceTag(c gateway.Context) error {
-	var req requests.DeviceUpdateTag
-	if err := c.Bind(&req); err != nil {
-		return err
-	}
-
-	if err := c.Validate(&req); err != nil {
-		return err
-	}
-
-	if err := h.service.UpdateDeviceTag(c.Ctx(), models.UID(req.UID), req.Tags); err != nil {
-		return err
-	}
-
-	return c.NoContent(http.StatusOK)
-}
-
 func (h *Handler) UpdateDevice(c gateway.Context) error {
 	var req requests.DeviceUpdate
 	if err := c.Bind(&req); err != nil {