feat(dashboard): update the dashboard design

[nimishavijay]

☑️ Resolves

• Add the background to dashboard section containers + blur when filled/mobile
• Fix some minor alignment issues

to be taken over @Antreesy

AI (if applicable)

• The content of this PR was partly or fully generated using AI

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

	🏚️ Before	🏡 After
Light theme
Dark theme

🚧 Tasks

• RTL
• Theming

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

---

🛠️ API Checklist

🚧 Tasks

• ...

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not possible
• 📘 API documentation in docs/ has been updated or is not required
• 🔖 Capability is added or not needed

[jancborchardt]

Looks very nice, as discussed! :) I am only concerned about file size

[jancborchardt]

Blocking til file size question is resolved

[Antreesy]

File size looks about the same as existing .png. WebP support alpha-channel, so I think we can reduce it by:

• separate icon from background
• make icon on transparent BG (only thing that need new assets)
• implement BG gradient with CSS (cheaper, but need original files to derive it)
• address RTL on JS/CSS side and drop duplicate assets
• remove old .png assets

@nimishavijay could you prompt it to split assets into icon+BG?