docs: update main readme and dev docs

[nicomiguelino]

Description

• Updates styling of headers and badges in README.md
• Added a link to the official Zapier Screenly integration
• Updated developer docs

Checklist

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation (where applicable).
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Copilot]

PR Overview

This PR updates the main README and developer documentation to improve visual styling and clarify the Zapier deployment process.

• Updated header formatting, logo sizing, and badge presentation in README.md
• Revised Zapier deployment instructions in docs/developer-documentation.md to streamline setup

Reviewed Changes

File	Description
README.md	Reformatted header and adjusted logo image width and badge presentation.
docs/developer-documentation.md	Added a new section for Zapier deployment while removing older instructions.

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (2)

README.md:6

• Verify that using a percentage-based width for the logo ensures proper responsiveness and visual consistency across devices. Consider testing this change across major browsers to confirm it renders as intended.

  <img src="assets/logo-full.svg" alt="Screenly for Zapier" width="90%">

docs/developer-documentation.md:161

• The updated deployment instructions only include 'zapier push' without referencing the initial setup commands (e.g., 'zapier login' and 'zapier register'). Clarify whether these initial steps are assumed to have been completed already or need to be executed for first-time deployments.

zapier push