docs: add Account Types page to Core Concepts

docs/builder/miden-guardian/core-concepts/account-types.md

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+---
+sidebar_label: Account Types
+sidebar_position: 3
+---
+
+# Account Types
+
+Miden supports three types of accounts, each with different visibility
+and state-management properties.
+
+## Public Accounts
+
+Public accounts store their code and state **on-chain**. Anyone can
+view the account's logic and current state, and anyone can execute
+transactions against them — similar to smart contracts on Ethereum.
+
+**Use cases:** Fungible token faucets, shared DeFi contracts, DAOs.
+
+## Private Accounts
+
+Private accounts store only a **commitment** (hash) to their state
+on-chain. The actual data lives on the user's device. The Miden
+operator never sees the account's internal state — only proof that
+a valid transaction occurred.
+
+**Use cases:** User wallets, privacy-preserving applications.
+
+## Network Accounts
+
+Network accounts are executed by the Miden operator rather than the
+user. They are used for notes intended for automatic network execution,
+where the user's device does not need to be online.
+
+**Use cases:** Notes requiring operator-side execution.
+
+## Comparison
+
+| Property | Public | Private | Network |
+|---|---|---|---|
+| State stored on-chain | ✅ Full state | 🔒 Commitment only | ✅ Full state |
+| Executable by anyone | ✅ Yes | ❌ No | ✅ By operator |
+| Privacy | ❌ None | ✅ Full | ❌ None |
+| Proved by | User / Anyone | User (local) | Miden operator |