Update Landing Page, improvements and patches

[gerteck]

Overview of changes:

Work to resolve #227

Also overhaul and update author guide to be properly structured, making it much more legible.

At the same time, also resolved some bugs:

• Fix stateManaged toggle bugs regarding default state.
• Fix bottom border showing up even when navigation headers toggled off.

And enhanced some functionality:

• changed the no-label attribute to inline for <cv-toggle-control/>
• Added description field to placeholders, updated settings interface for placeholders to match toggles and tabgroups (some hover animation, bordered)
• Added new card layout to placeholder-input component
• Added a pencil icon to the placeholder-input component, fixes placeholders: Give a visual cue for inline editable placeholders #158

Documentation wise:

• Cleaned up the structure of tab, toggle, placeholder, label author guide docs
• Updated the landing page
• Adapted the landing page to docs dark mode
• Add a nice logo row at the bottom

SEMVER impact of the PR:

• Major (when you make incompatible API changes)
• Minor (when you add functionality in a backward compatible manner)
• Patch (when you make backward compatible bug fixes)

Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No unrelated changes

Merge Instructions:

• For feature branches merging to develop: Prefer Squash and Merge.
• For release/hotfix branches merging to main, or subsequent sync back-merges merging to develop: ONLY use Create a Merge Commit.