refactor(verbose): replace the global flag and veprintln! with log

Diagnostics now go through the log facade: the library no longer
decides where output goes, and consumers plug in their own sink (the
CLI installs a stderr logger printing warnings always and ecr debug
diagnostics under -v; dependency records stay filtered out).  The
kernel 'quiet' flag moves from the global verbosity flag to an
explicit QemuConfig field.

crates/ecr-cli/Cargo.toml

@@ -22,5 +22,8 @@ clap = { version = "4", features = ["derive", "env"] }
 # Error handling
 anyhow = "1"
 
+# Logging facade; the stderr sink lives in src/logger.rs
+log = { version = "0.4", features = ["std"] }
+
 # Progress bar rendering of library progress events
 indicatif = "0.18"