refactor: layout/content, add description metadata, remove outdated re…

[roethke]

What changed? Why?
The get-started page contains unnecessary information for developers who already know why they are choosing to build on Base; the busyness detracts from their goal of easily finding the resources they need.

This refactor includes the following:

• updated theme from mint to aspen for a wider visual presentation
• updated primary color to use Base blue
• updated resource links using data on most visited pages in last 90 days
• reduced content on get-started
• added description metadata (LLM indexing)
• removed outdated references to Appchains, OnchainTestKit, Products and Use-cases
• replaced Smart Wallet with Base Account

Notes to reviewers

How has it been tested?
Locally

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1