feat(infra): structured leveled logging via tracing (#154) (#160)

Replace ~42 ad-hoc eprintln! with tracing + tracing-subscriber: HONKHONK_LOG-filtered stderr output (compact, ANSI on tty, no timestamps), level-mapped (decode failure -> error WITH file path; router chatter -> debug; first-run -> info; saves -> warn). Codex backup-gate review clean. Closes #154.

Author: thewrz

Cargo.lock

@@ -21,6 +21,8 @@ tray-icon = { version = "0.24", default-features = false, features = ["gtk"] }
 muda = { version = "0.19", default-features = false, features = ["gtk"] }
 gtk = "0.18"
 symphonia = { version = "0.5", features = ["mp3", "ogg", "vorbis", "flac", "wav", "pcm", "aac"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 thiserror = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"