restructure base-chain sidebar and file organization

[roethke]

What changed? Why?
Refactors the Chain tab documentation from a flat, noisy structure into a clean 4-pillar hierarchy that mirrors the file system:

• Sidebar: Consolidated into Quickstart, Network Information, Infrastructure & Operations, and Protocol & API
• File structure: Reorganized base-chain/ so directories match sidebar sections (network-information/, infrastructure/, protocol-api/); eliminated loose root-level files and legacy folders
• Content: Merged Configuration Changelog into Configuration page; consolidated duplicate RPC pages; transferred EVM diff content into Precompiles; moved why-base to get-started/

Notes to reviewers

How has it been tested?
Locally

[cb-heimdall]

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