standards: add core authorization primitives

[HDauven]

Part 2 of the Dusk standards stack. Base: #27

Adds the core Dusk-native authorization model:

• Principal for Moonlight, Phoenix, and contract identities
• runtime call context handling
• nonce and replay guards
• signed authorization envelopes bound to chain, contract, domain, action, payload, nonce, and expiry
• reentrancy guard security primitive
• client-side signed authorization construction example

Review focus:

• Phoenix vs Moonlight caller assumptions
• action envelope binding
• nonce/replay behavior
• exposed low-level unbound authorization helpers

Validation:

• make standards-ci