Add Persona-Based Top-Navigation Filter Bar

### Problem

New and prospective builders land on docs.hedera.com and are immediately presented with every topic at once. This overwhelms beginners, buries advanced content, and makes it hard to discover the “right first step” for each audience. Most of the tabs which are seen on the left nav is not relevant for a given reader.

### Solution

Implement a horizontal persona filter bar (in the global header, above the left-hand sidebar) with the tabs e.g.

Tab | Audience
-- | --
Native Service / Web 2 (SDK) | HTS / HCS / Schedule Service
EVM | Solidity / Hardhat / Foundry users
AI | Hedera Agent Kit / AI Agent Studio / Eliza plugin
Open Source Solutions and Integrations / Ecosystem | Studios / Oracles / Bridges etc
Tutorials / Cookbook | Development Guides

Note: this is just an example and can be adjusted

- Clicking a tab limits the sidebar to pages tagged with that persona.
- An analytics event records tab switches so we can measure adoption.

### Alternatives

_No response_