feat(ecc2): implement session create/destroy lifecycle (#764)

- Process spawning via tokio::process::Command
- Session state transitions with guards (Pending->Running->Completed/Failed/Stopped)
- Stop with process kill and optional worktree cleanup
- Latest alias resolver in get_status
- SQLite store migrations for state tracking

ecc2/Cargo.toml

@@ -36,6 +36,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 # Error handling
 anyhow = "1"
 thiserror = "2"
+libc = "0.2"
 
 # Time
 chrono = { version = "0.4", features = ["serde"] }