Remove Legacy Toast Message from V3 views

### Description:
We can currently see legacy-system toast messages on some V3 views after certain actions complete – for example, successfully logging in, logging out, editing the user profile, and so on.

[Green and Red Banners](https://www.figma.com/design/VhZHw3RudFNMzfPEEYchE9/UI-Kit---Foundations-Delivery?node-id=7009-91812&t=Bb3OQvjAfSIv29iU-4)
[Orange Banner](https://www.figma.com/design/VhZHw3RudFNMzfPEEYchE9/UI-Kit---Foundations-Delivery?node-id=474-4278&t=Bb3OQvjAfSIv29iU-4)

### Goal:
We want to suppress these messages on V3 views – the legacy experience should remain intact. Before removing anything, audit what's currently being shown and flag anything worth keeping.

**Suggested steps:**

- Identify and list all toast/legacy messages currently rendered on V3 views (login, logout, profile edit, etc.).
- Flag any messages that seem critical or user-facing enough to preserve, and raise them with @henryajisegiri for a decision.
- For banners we intend to keep, update the UI to match the banner style and colour (green, red and orange) in the Figma file
- For banners to be removed, remove the message banner from the V3 base template, scoping the change to the V3 flag so legacy views are unaffected.

Audit the V3 views mentioned in the issue, including login, logout, and profile editing, and trace their shared V3 base template. Compare rendered toast messages with the linked Figma banner styles, list anything potentially critical for @henryajisegiri to decide, and verify that intended banners are suppressed or updated on V3 views while legacy views remain unchanged.

Written by the indexing model from the issue text.