Make Date Added sorting work in results, or remove the option

**Problem**

Raised in the placement meeting as "companies aren't sorted by date by default".

The Apply lists are fine: the backend already orders profiles by `-id`, so they are newest-first.

The results lists are not. The filter sheet offers "Date Added" and "Alphabetically", but only alphabetical does anything. Option 0 is a no-op, because the sort only runs when the switch is 1. Neither results model carries a date field at all, so sorting by date is impossible client-side today.

**Where**

- `lib/resources/modelResources.dart:41-44` (the two sort options)
- `lib/viewmodels/ResultsCompanyWiseViewModel.dart:35` (sort guarded on `sortSwitch == 1`)
- `lib/viewmodels/ResultsBranchWiseViewModel.dart:35-39`
- `lib/models/companyConciseModel.dart:1-11` (no date field)
- Apply side, already correct: `omniport-app-placement-and-internship/views/company_profile.py:56`

**Expected**

Either the option sorts by date, or it does not exist. A control that silently does nothing is worse than no control.

**Fix sketch**

- Add a date to the results JSON generator, parse it into the concise models, and sort on it.
- If the generator change is not happening this cycle, relabel option 0 to "Default" and make the behaviour honest.

Start with lib/resources/modelResources.dart, the two results viewmodels, and lib/models/companyConciseModel.dart to trace the sort options, guard, and available fields. Check the results JSON generator before choosing the implementation path. Done means Date Added sorts newest-first, or option 0 is relabeled to match its actual behavior.

Written by the indexing model from the issue text.