Static Public Key Across Zites

**Is your feature request related to a problem? Please describe.**
What is the purpose of making a user's `public key` UNIQUE on every zite, but the `auth_address` _(aka Bitcoin address)_ the SAME on every zite?

**Describe the solution you'd like**
A STATIC `public key` (across all zites) that is derived from the user's `master key`, same as their `auth_address` _(aka Bitcoin address)_.

**Describe alternatives you've considered**
1. Could utilize the deprecated `auth_key`. (btw, why was this deprecated?)
2. Create a NEW plugin to derive a STATIC `public key` from the `master key`.

**Additional context**

## So Why Is This A Problem?

Dynamic zites work very well today, by allowing users to write data to their own folder/namespace within the zite's sqlite data storage.

But what if you're NOT using Zeronet's sqlite data storage. It makes using "legacy" client/server features within zites cumbersome; since you have to rely on "legacy" authorization techniques for the user. Rather, a Zeronet-enhanced APP SERVER "should" be able to retrieve a user's `public key` from a registry (based on their cert id) and then send a challenge that can ONLY be solved by the `private key` holder. This would be AUTOMATIC, upon arriving at a ANY zite, making user authorization __BUILT-IN__ for ALL developers.

eg. It should appeal to developers wanting to bridge an existing Clearnet application over to Zeronet. In which case, it would be ideal to utilize current backend systems while making the migration to a fully decentralized solution.

No files, tests, or entry points are named. Start by tracing ZeroNet's current public-key and auth_address handling, then review the deprecated auth_key mentioned in the issue. Done should include a defined approach for deriving a static key from the master key and clarifying how it supports authorization across zites.

Written by the indexing model from the issue text.