Eliminate double AnyProvider::clone() in embed_fn()

**Parent:** #620

## Problem

`crates/zeph-llm/src/any.rs:52-57` — `embed_fn()` clones the full `AnyProvider` once for capture, then again per call inside the closure. The inner clone is unnecessary.

## Solution

Wrap provider in `Arc<AnyProvider>` at the call site. Clones become pointer-sized.