Wire CLI agent loop: stdin -> Ollama -> stdout

[bug-ops]

Description

Connect all M1 components into a working interactive CLI agent.

Parent: #2

Branch

feat/m1/cli-agent-loop

Files

• crates/zeph-core/src/agent.rs — Agent struct with run loop
• crates/zeph-core/src/lib.rs — add module
• crates/zeph-core/Cargo.toml — add zeph-llm dependency
• src/main.rs — bootstrap: load config, create provider, run agent

Acceptance Criteria

• cargo run starts REPL (prompt: "> ")
• Messages sent to Ollama, response printed
• Multi-turn: previous messages included in context
• Ctrl+C or "exit"/"quit" exits cleanly
• Ollama unreachable: error message, not panic

Depends On

#9 (Ollama backend), #10 (Config loading)