fix: add clock feature to chrono in zeph-memory

[bug-ops]

Problem

After workspace dependency reorganization (#1959), the zeph-memory crate was missing the required clock feature for chrono. This caused cargo publish --dry-run verification to fail with:

error[E0599]: no function or associated item named `now` found for struct `Utc` in the current scope
error[E0599]: no method named `format` found for struct `DateTime<Tz>`

Solution

Add features = ["std", "clock"] to the chrono dependency in zeph-memory/Cargo.toml. These features are required by:

• chrono::Utc::now() in src/semantic/recall.rs
• DateTime::format() in src/router.rs

Validation

• ✅ cargo publish --dry-run --workspace --allow-dirty --features full now passes
• ✅ All features verify correctly for all 14 crates