docs(context): tool_result_compress module missing from zeph-context lib.rs module-level docstring

[bug-ops]

Description

crates/zeph-context/src/lib.rs module-level docstring lists all public modules except tool_result_compress (added in #4021/08021eeb):

```rust
//! # Modules
//!
//! - [budget] — ...
//! - [manager] — ...
//! - [assembler] — ...
//! - [input] — ...
//! - [slot] — ...
//! - [summarization] — ...
// tool_result_compress is missing from this list
```

The module has its own excellent doc comment, but the crate-level index doesn't reference it.

Fix

Add one line to the # Modules section in crates/zeph-context/src/lib.rs:

```
//! - [tool_result_compress] — Acon per-result and batch-level token budget enforcement
```

Environment

• Commit: 08021ee
• CI-889 arch audit