[FE] Add tracked refs filter to project dependency list
## Summary
Hook up the `securityTrackedRefs` query to populate a filter dropdown on the project dependency list, and pass selected values as `trackedRefIds` / `trackedRefsScope` to the `getProjectDependencies` query.
Design: https://gitlab.com/gitlab-org/gitlab/-/work_items/599746#note_3388260696
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## Context
- Spike issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/599746
- FE implementation thread: https://gitlab.com/gitlab-org/gitlab/-/work_items/599746#note_3410397216
- BE MR (GraphQL schema with `trackedRefIds` / `trackedRefsScope` arguments): https://gitlab.com/gitlab-org/gitlab/-/merge_requests/234558
- Parent epic: https://gitlab.com/groups/gitlab-org/-/work_items/18681
## What needs to happen
1. **Create a new `tracked_ref` filter token** in `project_dependencies_filtered_search.vue`, gated behind the `securityDashboardTrackedRefFilter` and `vulnerabilitiesAcrossContexts` feature flags.
2. **Fetch the tracked refs list** using the existing `securityTrackedRefs` GraphQL query:
```graphql
query {
project(fullPath: $fullPath) {
securityTrackedRefs(state: TRACKED) {
nodes {
id
name
refType
isDefault
}
}
}
}
```
3. **Pass selected values** as `trackedRefIds` and/or `trackedRefsScope` variables to the `getProjectDependencies` query.
4. **Update `project_dependencies.query.graphql`** to accept the new `trackedRefIds` / `trackedRefsScope` arguments (the BE schema already supports them).
5. **Wire up the filter** through the Vuex store (`buildGraphQLFilterOptions` in `actions.js`).
## Notes
- The BE schema already accepts the arguments, but the actual filtering logic will land in a separate BE MR. The FE plumbing can be ready ahead of that.
- Follow existing filter token patterns (e.g., `component_token.vue`, `version_token.vue`).
## :question: Unknown
Just realized we may need to have a persisting trackedRef token if the default branch should always be the default. Need to explore into this
## MR Series
1. Pass default branch to FE: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/239307+
2. Display trackedRef option: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/240011+
3. Pre-select Token with default branch: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/240336++
4. Initialize dependencies with default branch (GraphQL): https://gitlab.com/gitlab-org/gitlab/-/merge_requests/240340+
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