Initialize Cargo workspace with 4-crate skeleton

[bug-ops]

Description

Create the Cargo workspace with virtual manifest and 4 library crates plus the binary entry point.

Parent: #1

Branch

feat/m0/workspace-bootstrap

Files to Create

• Cargo.toml — workspace root (resolver 3, edition 2024, workspace deps, lints)
• src/main.rs — binary entry point
• crates/zeph-core/Cargo.toml + src/lib.rs
• crates/zeph-llm/Cargo.toml + src/lib.rs
• crates/zeph-skills/Cargo.toml + src/lib.rs
• crates/zeph-memory/Cargo.toml + src/lib.rs
• config/default.toml — minimal config placeholder
• skills/.gitkeep
• .gitignore
• CHANGELOG.md

Acceptance Criteria

• cargo build succeeds
• cargo clippy -- -D warnings passes
• cargo test passes
• cargo run prints version
• Workspace lints: clippy::all + clippy::pedantic = warn
• Author in manifests: bug-ops (from gh auth)