Add application layout images to README via docs/assets

[Copilot]

The README did not include the requested visual layout references from docs/assets. This updates the documentation to surface the application’s primary visual variants directly in the top-level project overview.

• README documentation update

  • Added a new Application Layout section near the top of README.md.
  • Embedded three image references for quick visual orientation:
    • docs/assets/horizontal.svg
    • docs/assets/stacked.svg
    • docs/assets/icon.svg
  • Tightened alt text for clarity (OpenCalendar icon).

• Repository asset alignment

  • Added docs/assets/ and populated it with the referenced SVGs so README links resolve in-repo.

## Application Layout

General visual layout assets:

![OpenCalendar horizontal layout](docs/assets/horizontal.svg)
![OpenCalendar stacked layout](docs/assets/stacked.svg)
![OpenCalendar icon](docs/assets/icon.svg)