Add a home dashboard tab

**Problem**

Raised in the placement meeting. The app opens directly onto the Apply tab. There is no landing screen giving a student their status at a glance: credits left, open applications, upcoming deadlines, recent results.

**Where**

- `lib/screens/home/homePage.dart:89-96` (four tabs, no dashboard)

**Expected**

A home tab summarising the student's current placement state.

**Fix sketch**

- Add a fifth tab, or make the existing first tab a dashboard.
- Most of the data is already fetched by existing viewmodels and can be composed without new endpoints, except the aggregate stats.

Depends on the stats work for the aggregate portion.

Start with lib/screens/home/homePage.dart:89-96 and inspect the existing viewmodels that fetch placement data. Check the dependent stats work before deciding whether the first tab or a fifth tab should become the dashboard. Done means the app opens to a home summary showing credits left, open applications, upcoming deadlines, and recent results without disrupting existing tab navigation.

Written by the indexing model from the issue text.