docs(overview): fix terminology and improve clarity for developer onboarding

[Giri-Aayush]

Summary

This PR improves the Aztec Overview page from the perspective of a developer who is new to Aztec. As someone onboarding into the ecosystem, I noticed several terminology inconsistencies and areas where the language could better guide newcomers through Aztec's unique concepts.

Changes

• Terminology: Replace incorrect "Public VM" references with "AVM" (Aztec Virtual Machine) and "sequencer" to align with official architecture docs, diagrams, and the public execution documentation
• Grammar: "A incoming/outgoing" → "An", "get start" → "get started", "follow" → "follows", "transactions" → "functions" where referring to execution context
• Execution section: Restructured from a dense paragraph into scannable bullet points with a clear directional flow (private first, then public)
• Private state section: Rewrote with a cash analogy to help developers unfamiliar with UTXO models understand notes and nullifiers intuitively. Reordered to explain public state first (familiar to Solidity devs) before introducing the new UTXO concepts
• Account abstraction: Improved wording for natural readability
• PXE/AVM separation: Consistent use of "AVM" instead of mixing "Public VM" and "AVM"

Why both docs-developers/ and versioned docs?

Applied changes to both docs-developers/overview.md (next version) and developer_versioned_docs/version-v4.0.0-devnet.2-patch.0/overview.md (current stable devnet). The fixes improve clarity for current users on the stable version too. Happy to drop the versioned docs changes if the team prefers to keep those frozen.

Test plan

• Verified locally with yarn start that both devnet and next overview pages render correctly
• Confirmed terminology matches official architecture diagrams and the public execution, transactions, and call types documentation